This is where you and I often butt heads. Fast Cast is indeed an "Interrupt", and in the context of story and pacing, should indeed be the means by which you can save your grog from being sliced and diced.
I would love to hear other peoples thoughts on this specific aspect of Fast Casting 
It's a bit disingenuous to say that my position doesn't allow you to save your grog from being sliced and diced. I'm saying you can't save him from being sliced and diced with a PoF. As a response to an event, the event being the grog sliced and diced, means turning the sword away or transporting the grog to not be where the sword is. It does not mean somehow being able to deliver a devastating attack which preempts action the opponent would have taken, when you would not normally have been able to do so. Yes, you can certainly have your magus cast Pilum of Fire at the opponent slicing and dicing your grog, but that doesn't stop your grog from being sliced and diced. Going back to the rules, it's a response to an event, and I believe the event is your grog getting hit, not the swing of his sword. There are any number of spells that I would rule could be effective in negating the attack. I'd be more inclined to allow a preemptive PoF if you have delayed your action from a previous round or delayed your action if you won initiative, but that, IMO, is a bit beyond the normal rules for fast casting, as it is from a supplement.
So let's go into interrupts, since you brought it up. Rules for interrupts are added in Lords of Men, and even then, one must have won initiative and delayed action or delayed their action from the previous round to interrupt an opponent's action. Our discussion came up in the context of the Dimicatio, so delaying action in the event you didn't win initiative would be kind of moot. And if you won initiative, you'd probably want to attack first in the Dimicatio, not delay action to see what your opponent would do.
Actually, you have me confused with someone else 
My own HR is as follow:
- Separate among different targets: everything works as normal
- Piling all on one: Each extra copy adds 5 to damage / strips 5 more might.
Save thatk, IIRC, it also says that interrupts works like fast cast...
No, it says it is similar to the way fast casting resolves. And, if someone wanted to delay action to cast a spell preemptively, it is altogether different So examining fast casting nothing is ever said that fast casting can negate or prevent an event, and the example of two magi casting spells at each other demonstrates this, the opposing spell is cast, and it is up to the other magus to negate the effect.
This is why I brought up Dimicatio as a specific example. I truly feel that things have someone gained a life of their own. I understand what was intended from David's comment. But according to other canon sources, regardless of what was intended, that was not what is RAW. My understanding is that the intent was not to allow a formulaic spell in the same round as a fast-cast spell but that the actual rules ended up being that you can do a formulaic spell in the same round as a fast-cast spell. As far as I can tell that seems to be the only interpretation that maintains consistency.
Chris
It's nothign new here. At least we're still on the general topic of fast casting.
Well,I'm glad I asked the question.
If anyone cares I ran the session on sat. My players are role playing their way as apprentices. This week the challenge/adventure was a tournament similar to the Dimicatio.
And what was the moral of the story you might ask?
It seems nearly every player used Quickness as a dump stat. It made for some very funny and creative fast casting duels.
Quickness can be a dump stat for sum magi. But if you're building a magus at all interested in combat, you can't ignore it. If you're building one who excels at combat, then it needs to have a much higher priority than other stats, and might also cause a magus to not make Int +3. 
And maybe select the Virtue Fast Caster.
That being said, high Finesse goes a long way for making up for treating Quickness as a dump stat.
The debate here is then what constitutes a "Response to an Event". I say that the event being responded to is not the actual slicing-dicing. It is, as you said, the swing of the sword. Or drawing the sword from the scabbard. Or taking a step towards the grog. Thus, I would put forth the proposition that, perhaps for you, it is more a matter of aesthetics. You prefer a game about occult mystery and arcane intrigue. You do not like comic-book superhero magi or old-west gunslinger types, and you do not find that style of combat realistic.
And I will admit that I myself do prefer high action/adventure. So perhaps it slants my PoV the opposite way and neither of us are in the correct middle-zone.
As an SG, I do prefer a narrative approach and would advocate erring in favor of the players. If the grog is wearing a Red shirt, then kill him. If the grog is a beloved charater and a favorite of a player, save him.
But let us not debate with each other. I would like us to debate with other people and get them to debate. It is a thought experiment. You and I each advocate our specific position, and see what the mass of our peers thinks about it.
Markoko's Position
- Fast Cast spells can be used as an "Interrupt"
- "Responding to an Event" is deliberatly ambiguous. It could be a spell cat at you, someone suddenly moving, a bird flushed out of a bush (Hermetic skeet shooting should be an event
), someone coughing or twitching (which I agree would mean that your character is in a hyper-alert state, meaning the player has indicated he is maintaining an alert status and is ready to react if his opponent makes a move) and etceteras. - If the Fast Cast roll beats the opposing initiative, then the effects of said spell are applied before that opposing action, and if if the opposition is rendered ineffective or eliminated then that action never happens.
*Case in point: A thug is attacking your buddy with an axe, and you Fast Cast a PoF to stop him. If the Fast Cast roll succeeds, and the blast kills the opponent; the guy drops dead as he is heafting the axe or pulling back for a swing, not in mid-swing or as the axe is coming down on your buddy's head. - Wining Initiative is always more advantageous, I agree, and is worth spending Confidence on. It is a static number and remains fixed, and a good Initiative makes it much more difficult for an opponent to Interrupt your own actions with Fast-Casting
[quote="Marko Markoko
Markoko's Position
- Fast Cast spells can be used as an "Interrupt"
- "Responding to an Event" is deliberatly ambiguous. It could be a spell cat at you, someone suddenly moving, a bird flushed out of a bush (Hermetic skeet shooting should be an event
), someone coughing or twitching (which I agree would mean that your character is in a hyper-alert state, meaning the player has indicated he is maintaining an alert status and is ready to react if his opponent makes a move) and etceteras. - If the Fast Cast roll beats the opposing initiative, then the effects of said spell are applied before that opposing action, and if if the opposition is rendered ineffective or eliminated then that action never happens.
*Case in point: A thug is attacking your buddy with an axe, and you Fast Cast a PoF to stop him. If the Fast Cast roll succeeds, and the blast kills the opponent; the guy drops dead as he is heafting the axe or pulling back for a swing, not in mid-swing or as the axe is coming down on your buddy's head. - Wining Initiative is always more advantageous, I agree, and is worth spending Confidence on. It is a static number and remains fixed, and a good Initiative makes it much more difficult for an opponent to Interrupt your own actions with Fast-Casting
[/quote]
I find myself in agreement with Marko's position, this is how I've always envisioned it.
And even if the PoF does not fell the attacker immediately any wound at all hampers his subsequent attack on your trusted grog, who needs any help he can get.
However I also believe I like the optional Initiative rules from Lords of Men. In theory that is, because I haven't tested it. But I like the idea that a very high or low Initiative does not make or break the action scene. A single dice roll should not IMHO be so very important, I'd rather have contested Priority Rolls made each time someone tries to interrupt another or react to his action.
My position does not prevent a magus from casting PoF. It just doesn't negate the action being responded to. The PoF will arrive just as or just after the grog has been sliced and diced. This can be advantageous for subsequent rounds, as you suggest, but it doesn't counter the attack. Other spells could do a much better job and actually negate the attack. The example of fast casting in the MRB shows a spell being cast and the response is a counter to the spell to prevent the spell from reaching the intended target.
Lords of Men allows one to interrupt an action, yes, but again, to do so, you mist have had a higher initiative and chosen to delay your action. If that's what is going on, I don't have an objection.
Ars combat is deadly, favored grogs die. Everythinng has a season. But if, as I have said to Marko, he wants to be responding to the opposing grog pulling his sword, well, that's good for the other side, too.
But if your Fast Cast is fast enought to use Rego Terram to deflect the sword, then the spell happens before the attack. I'm just saying that using to respond with PoF instead also happens before the attack - does not negate it (unless the attacker is killed) - but affects his attack, say by the Wound Penalty.
Serf's Parma, don't have my books with me now but I have some notes for Lords of Men:
You seem to be mixing up Delaying Actions and Interrupting Actions. Sure, the grog can delay his action so he can charge to intercept once he sees the enemy charging one of the magi. But it's another thing to cast a Fast Cast spell, LoM specificically says this need not be Delayed. But you could Delay your regular action to "hold a spell ready". In the example above the magus Delays casting a spell - let's call it PoF - to attack the first enemy to begin moving. It's not Fast-Cast so does not suffer the penalties and restrictions for this. Yes, it might not prevent the enemy from completing his charge and attacking, but it'll hurt him. Also, I'm not advocating that the magus Delaying also gets to Interrupt and Fast-Cast. But after his Delayed action he could Interrupt and Fast-Cast at another of the enemies takes an action.
My primary issue with this is that it is sauce for the goose. If I open this up for PCs, it's available for NPCs, too. Players tend to view rules changes as a net win for them. In this case, against the opponents they are facing it is a net lose. I dislike strongly that anyone can beat their own initiative later on and then act with impunity (including my NPCs). If the objection is that a single roll impacts things to greatly, that's relatively easy to fix, roll initiative every round. Don't some games do that?
Mark and I butted heads about this, primarily about how he understood fast casting and the Dimicatio. In that instance he wanted to cast a spell at the moment his opponent (assuming the opponent won initiative) uttered his first word, to try and beat his own initiative. Then why can't his opponent do the same thing? It becomes a thing where you do a bunch of die rolling to figure out who's really going first. That is kind of boring, and it isn't at all narrative. This is in Dimicatio, a one on one situation.
In a group on group scenario, magi shouldn't really be paying attention to their grogs, they're supposed to be paying attention to the big bad, or working on the grogs that their grogs can't touch, perhaps, with a more area of effect spell that might cause the other side to run away or something. Point being, if Marko's character is ultra focused on what is happening with his shield grog(s) he isn't focused on something else. You cannot simply watch everything on the battlefield at one time. As an SG, I'm doing you a solid by letting you know your grog is getting sliced and diced, giving the player and the character an opportunity to act[1]. Your best spell is Pila of Fire, but of course, the opposing grog is already in mid swing, so the only thing you can do is something that negates the attack, like moves the sword, or blocks the sword, or translocates the shield grog, or the opposing grog. I've been dinged by not calling this cinematic or it is not high action or adventure. I counter that mine is higher action and higher adventure, because it is forcing players to make interesting (and hard) choices. What's more interesting? The magi saves the day, again, with his preemptive Pila of Fire? Or he just barely manages to spontaneously relocate the opposing grog so that his swing makes contact with the big bad, instead of his own shield grog? It's about thinking a bit more broadly. I don't have a problem with Pila of Fire being a bread and butter spell, but that's like looking at all problems as nails when you're holding a hammer. They simply aren't. There's no reason you can't use your defensive spells in interesting and offensive ways, I enjoy that, I think it's fun, I think it raises the stakes a bit. But what is good for the goose is always good for the gander. My job as SG is to make things interesting. I don't find opposing dice rolls until someone loses interesting or narrative. You have to trust me, as SG, that I'm not going to always kill the grog straight out. Maybe he lingers on. Maybe he's maimed? Maybe you can share one final moment with him, and tell him, "By Grabthar's Hammer, you will be avenged."
[1]If a player wants to say that they are hyper alert and watching everything, that can be countered with you guessed it, more opposing roles. Awareness to catch what the other guy does when your looking over another part of the battle field. At some point, you have to trust the GM/SG. And if the SG is telling you you really don't want me to interpret the rule that way, there's probably a really good reason behind it.
I think the key is that the Fast cast does not prevent the other spell from being cast. It does not supersede initiative. There is nothing that suggests that it changes initiative. The other action is going first. but a fast cast spell will be nearly simultaneous. Thus it can deflect the blade or cancel the cast spell.
Delayed action is just that. You won initiative and have decided to wait until something happens. Being an old Champions player, I would force people to name the trigger. " I wait until the archmage's action." "I wait until the knight acts." Now you can do something and your initiative is still higher than the trigger action. It does not prevent the mage who is delaying their action from fast casting a defense. But you can't wait for the trigger than fast cast and cast your formulaic spell. It is not in the spirit of the rules. Fast cast is in reaction to and delay is triggered by.
And this is where things get dumb IMO.
I could go along with JL's interpretation, save for 2 points:
- If you can't kill someone in mid-swing, which should at least mitigate the damage he does with his sword*, but always at best as he completes his swing, how can you be fast enough to, say, actually block his sword or translocate your pal before it? This is not consistent.
- Worse: All his interpretation rests on one point: You're trying to stop a very quick action that's already engaged. Yet, an action doesn't have to be that quick and can simply be running from point A from point B, as long as it's done in one round. If, say, a grog run the whole round towards a mercere portal and you must stop them. JL's interpretation would have that, disregarding formulaics, the only way to stop him would be with a non-lethal fast-cast spell, even if you managed to cast it as soon as he took his first step towards the portal. I just can't see that. This also works for swords, in that you don't always land 1 blow every 6 seconds. Sometimes, the attack roll represents the result of an exchange of blows that is spread over the whole round.
- Especially as, IIRC, you can do that with delayed actions, by stating that, say, you target the first guy who strikes at your pal, which is a reaction to an action. So, if reacting to an action, sometimes, you can kill a guy before he's completed it, and sometimes you can't.
I do agree, but this is why Awareness is for, and the more confused the battle, the harder the rolls.
If you don't want to roll dices, you could ask players to specify a number of things they keep tabs on equal to, say, Per + Awareness (min 01) and roll with it.
From my experience with weapons, this is actually reasonably consistent for weapons. In fencing you are far, far more likely to get struck (and in foil or sabre lose the point) when you try to do this. (In epee you would both get the point.) Combine this with the fact that instantaneous death is very hard to pull off, and it's all that much more likely this fits reality.
I think the rest of this point and the other points are fine. But I do think there are issues both ways. Ultimately this comes down to the game not being able to distinguish well between how long it takes you to react to an event and how long it takes you to complete that reaction. The during part is missing. Things are too sequential. While I'm happy with systems that handle the during part, I doubt most players would be. So these are simply issues I expect to encounter and expect to be YSMV.
Chris
Your argument here, if I may reframe it is, you don't like my system of limiting the kinds of actions that can be taken to negate a combat result, and would rather substitute it with some method of awareness checks. I'll point out that awareness checks are an arbitrary result, and still governed by SG fiat, to a certain extent and all they do is move the point of contention from the saga's overall mechanics and rule framework to a case-by-case decision for every combat result that the players don't like[1]. That's really bad, and not at all cinematic, as you have outlined previously in this discussion and I've outlined how that system can fail below. My alternative is also outlined in a specific scenario below the second point below[2]. I'm not saying that either system is bad. I'm just saying one system is much easier to administer, and it is also much easier for everyone to know where they stand with respect to the actions possible, and their limits. Players can consistently take action, without the need for awareness rolls that might allow them to save other characters, should they choose to do so. Players aren't bound to the fickle winds of fate based on the results of an awareness check, and don't annoy the SG. It's clean, and clear cut.
[1]I can see things like the following, SG in blue, player(s) in red.
Last time an awareness roll that high was enough to save him.
But thecircumstances are different this time.
"How?"
"There was smoke in the air, and Roberto was facing off against three goons.
"But there was that one time there was four goons, and it was dark out.
"Argh..."
((At this point the SG either gives into players (which is bad, too) or he digs in his heels.))
[2]
Carlos is hit, it looks bad. If you guys can come up with some way to mitigate the attack, you can check to see if you can fast cast a defense.
(players discuss some things, ask questions about the overall tactical layout, ask the SG to rule whether another magus could use Wizard's Leap to leap into the fray and take the blow on himself)
"That's possible, I'll give it an even chance of succeeding if your fast cast roll and spell are successful. Let's do the rolls in order, if you're going to commit to that course of action."
"I think it's our only choice guys, or we let Carlos die. I think I can soak the damage."
Player rolls successfully for fast cast timing, and the spell, and then finally rolls an even number and successfully leaps into the fray, absorbing the overwhelming blow that would have certainly killed Carlos, but only does a light wound to Alexei, due to his insane soak.
Not sure if that will add anything to the debate, but here's how I see fast-casting working.
I think it's a matter of intent and timing, description-wise. Basically, at which point is the player declaring a fast-cast spell? If it's before the result of an action is known, I would allow it to prevent that action by preemptively killing the source. If the fast-cast is annouced after the result of the action, I would force the fast-cast spell to be targeted at the action to prevent it, rather than by an attack on the source of the action. Let's take a combat scene.
In a slightly different situation, the same magus could have decided that the important was to take out the second bandit instead of saving the grog, and used a second fast-cast Pilum. His grog would have suffered the full effects of the axe swing just as the bandit got engulfed in flames (mutually assured destruction).
So, to repeat myself, fast-casting can only preempt an action if it is called before the results of the action is known. The same would be true if an opposing magus was casting a spell at the grog in the previous example. The player could decide to fast-cast a spell to take out the magus before knowing what the effects of the spell are, but once the spell is cast the only way to prevent it from taking place it to target the action. You can no longer prevent the result by killing the source.
To add to the above. The Bandits won the initiative. Fast-cast in response to the attack on the grog. The grog still gets attacked but you can spont a PoF and damage the Bandit. It CANNOT go before the bandit's action because the mage lost initiative. The mage still gets their formulaic PoF on one of the other bandits during his initiative.
My own preference is to let magi use fast-casting as a "trump card" during combat, emphasizing their great power. So -
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The fast-cast spell may be cast at any time in the round, as you may "react" to anything. This includes your turn - you may fast-cast on your turn, or anyone else's.
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Combat is cinematic, not realistic. You don't need to "notice" that you need to fast-cast to save your companion's life, or to focus through the haze of combat, or so on. You just react to the combat as it is told around the table. (You'd still make to make Awareness rolls to spot an ambush or so on, of course.)
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You can fast-cast any effect you want to (and can). I like the idea of limiting cast-casting to defense, but find that it makes no in-character or in-world sense.
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You can fast-cast in reaction to a fast-cast. I don't like it, but I can't see how it can be reasonably avoided without rendering fast-casting incapable of averting a fast-cast attack.
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If cast as a reaction to another action, which is not yet resolved, the fast-cast spell can stop that action from succeeding. Thus, if you fast-cast a pilum of fire at a foe attacking your companion, you can burn him before he makes his attack.
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Fast-casting still cannot change the past. If the action is already resolved, it cannot avert it. If the attack hit, it instantaneously does damage and you can't do anything in "between" the hit and the damage as there is no time for that.
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Fast-casting doesn't hinder your normal casting. You can fast-cast a defense and then normal-cast an attack spell in the same round. This is not RAW as I read it, it is however how I played it.