Concentration rolls, how do you use them?

Core rules page 82 has the rules for Concentration rolls. If there is some distraction magi need to roll Stm+Concentration or spell won't go off (stress dice are still rolled just to check for Botches). The table lists Ease Factors, from 0 for standing still up to 15 for being injured. Ouch!
The list mentions walking, running, dodging, being jostled. But why list a difficulty for Standing Still, what constitutes the distraction that demands a roll here? Do you always need to roll for the normal chaos and noise of a fight? Ease Factor 0 still makes sense though, since a Stm -3 Conc 0 magus could still fail without Botching.
But if you move around at all, just walking you need to roll 3, or 9 for running.
If you attempt to Dodge that's a 12, and better hope you succeed because being injured is 15. Injury is a binary thing, it doesn't matter if you receive a light or 5 heavy wounds.
Being jostled is 9. This sounds to me like being pushed or bumped into - why is dodging harder?

This is for immediate effects, for being able to cast a spell while something happens to you or you do something.
For ongoing situations the roll is said to be 3 points easier, there is a table with these situations. Like when you have a D:Conc spell going and do something. Short yes/no answer warrants an ease factor of 12. Conversation or casting another spell is 15. Having an injury is 3x wound penalty.

A player in my group has been wondering how published combat magi pull that off, since e.g. famours Philipus Niger only has Concentration 4.

How do you people run this kind of thing?

I consider still to be the starting point. Not that a roll is needed, it's just the baseline. Dodging should be harder than jostled, in Ars, dodging is evading an attack. Jostled would probably happen if your shield grog botches...

And that brings us to the importance of shield grogs, they are important, leave them at the covenant at your peril.

During combat, one doesn't need to roll concentration, if you aren't being attacked, or otherwise injured.

For some perspective, average EF isn't hard to get to. Roll of 6, stamina+concentration + mastery score ( if imperturbable is a mastery ability)=3. And a lot of magi have 2 stamina.

It is true that the encounter in question where I attempted to enforce it per RAW (or at least what was understood from it) featured magi noticeably lacking a Shield Grog as Defender.

Even if Concentration rolls are only needed for physically disturbing the magus - i.e. not for noise, blazing fires or whatever - being physically attacked and attempting to dodge means you're hard pressed to get the spell off! Ease Factor of 12 (for dodging) or 15 (if injured same round as casting) is hard even for a Stm +2 Conc 3 magus, especially since Wound Penalties count, and if you need to toll for having been 'injured' that's at least -1.

This also makes one wonder when and how injured this round should be interpreted. The abstract way the initiative system works may lead to odd results unless you rule this as injured since your last action because then no matter who rolls highest you might get affected. If the magus rolls higher Init than the beast he is fighting then he casts his spell before the beast injures him, and next round he does this again...

But if Concentration rolls are needed because the magus needs a few seconds to wave his arms in order to cast, then a Fast-Cast defense shouldn't require this, even if you were injured since your last action, and you are responding to another Init count before your regular action comes round again. The nature of Fast-Cast should mean the action is brief and therefor not prone to interruption by injury etc. as normal spellcasting is?

"Injured this round" applies to cases where you're maintaining D:Conc on something, if I'm not mistaken. Doesn't happen when you're casting a spell under any circumstances I can think of (noble's parma here).

Philippus Niger has a fairly high Concentration for a magus, but the vast majority of his spells don't require it. He solves most fights by casting one spell, after all.

No, it doesn't. Check the headings under that chart on page 82. One is for casting a new spell, one is for maintaining concentration on an existing spell. Being injured appears in the former. We're you injured this round, if yes, you must succeed at the concentration check for spell casting.

Yeah, his concentration total is 6, which means he has an even chance of handling most hard rolls. Further, he is Self-Confident and can burn confidence whenever his player rolls a two.

That's not exactly sustainable in the long run*

*[size=85]unless you use certain tricks from RoP: Infernal[/size]

Actually, if he uses 2 confidence points per session, it is entirely sustainable under the guidelines established for granting them:

There are some situations where one has to burn a lot of confidence, because the dice don't go the player's way, but even then, there are times where the player need not burn any confidence during a session and gains a couple. My Self-Confident combat maga has 10 points right now. She burned two last session against a magus to get through his penetration, and gained two for ultimately winning, and resolving a personal goal. So no tricks from RoP:Infernal needed.

In my rantings I'm almost exclusively talking about Concentration to cast a spell, not the rolls every two minutes for when a D:Conc spell is active.

Okay sure, there is Confidence. But those points are limited in number, and require you to actually gain some. If the SG remembers to award them (which may not happen, especially if players forget to use them), if you burn through 3-4 in a single encounter this is IMHO not sustainable, unless your SG dishes out a lot more than we're used to. Self Confident may be a popular choice for that extra oomph when it really matters but it is still a an active choice and not all magi have this.

Being injured requires a Stm+Concentration of 15. Assuming an average die roll of 5 plus Confidence your Stm + Concentration still needs to be 7. Actually even higher, since that injury surely inflicts Wound Penalty on you and thus modifies the roll. Sure, you're not injured every round, but other rounds you may be dodging to avoid getting hit which is still an EF of 12. Since you can't be using Confidence every round this gives similar numbers.

Note that the table also has an entry for sudden noise of flash of light, and this I assume means things that actually surprise you. So that the magus you're fighting casts BoAF is expected, but if his servant sneaks up behind you with a device of BoAF...

I'm not really questioning the rules for Concentration Rolls - well a little - but mostly asking how many people enforce this and what their experiences are?
What is the Concentration score of your combat magi?

As additional information I point towards Normandy Tribunal's bad-ass magus Rotigers of Tremere - Montverde's chief combat magus. IIRC his Concentration is 3.

It seems to me a magus, barring one protected quite well by a Shield Grog or one with high Concentration ability, is likely to fail casting spells quote often. A magus designed towards combat and action is likely to have a positive Stm since he is likely to want to pull off his spells with a decent Penetration, and this helps with Concentration as well with Soak. He is advised to prioritize Concentration ability however, and perhaps to keep training to lower the odds of missing out on a round of casting. Ease Factors do not increase for the more challenging encounters with more powerful beasts or persons, although increased ability scores or better powers may be harder to avoid and therefore increase the frequency of being hit.

Luckily Concentration is a General Ability so books on the subject may be bought with merely vulgar silver rather than precious vis.

Oh, and how do people view Concentration rolls for Fast-Cast Defenses? Are they required if you've recently been injured or are dodging?

Exempli Gratia:

Titus of Flambeau and his party are traveling through Schwarzwald to get to Durenmar, when suddenly they are ambushed by a group of Zee Nazty Bockmänner!

Bockmänner win the Init witn 18 vs. Titus' 7.

Round 1
Count 18: Bockmänner charge in for an attack.
Titus reacts with a Fast-Cast spell to block off his attackers. He does not need to roll Concentration since there is no distraction, and this is Fast-Cast not a regular spell being cast, which takes several seconds. It works but only one of the two Bockmänner is blocked, leaving the other to attack. This attack is succesful and Titus injured.

Count 7: Titus cast a spell but needs to make a Concentration roll of 15, since he was injured. This is a hard roll to make.

Round 2
Count 18: Bockmann attacks, if Titus wants to try another Fast-Cast defence does need to roll Concentration for being injured? He was injured last round, but because Initiative is an abstraction of actions of about 6 seconds happening more or less simultaneously or at least with overlap. Is the injury a distraction from the time of the Bockmann's attack in Round 1 over the course of anything happening up to the time of the Bockmann's action in Round 2?
Anyway, assume Titus is hit again.
Count 7: Titus now needs another Concentration roll because he was just injured. Again. Since Concentration rolls have no exceptions from Wound Penalties these rolls quickly become more and more difficult to pull off. Actually, the table for Continuing Situaitons special rules here only for injuries, which IMHO implies they are used normally for other Conc rolls.

Even if Titus has not been injured he would still have had to roll vs. a 12 for dodging. Otherwise he was sure to have been injured. Of course, a Fast-Cast defence could have blocked the attack so he would neither have been dodging nor injured thus avoiding Concentration rolls. Or he could have used a [strike]meat shield[/strike] Shield Grog as Defender and also avoided this. Against formidable opponents a Shield Grog can also quickly be worn down by Wound Penalties, but at least it buys the magus some time to cast spells with a lot less distraction and hopefully dealing with the situation.

FWIW, I wouldn't apply wound penalties on top of the very hard concentration roll. That's double penalizing, and they will have penalties on casting. That's enough for me, as an SG. They have to make a very hard concentration check, and then they still have to cast a spell with their wound penalty. It's not too uncommon for SGs to double penalize, by setting an EF too high, and the applying other penalties to the roll. Now, I would add botch dice to the concentration roll based on the wound penalty. If you mess up, it's gonna be glorious.

My primary combat maga has a concentration score of 3, and Stamina of 3, spell concentration specialty. We also have a house rule that the silver cord aids in concentration checks (this is a very useful and thematic house rule, IMO), that silver cord score is 1, so she has an effective 8 on concentration checks. She's a weather maga, and a lot of the Auram spells are Concentration duration, so it seemed appropriate, it's helped out in other areas, such as when her shield grogess was one-shotted (surprise!).

Fast cast spells are a mess, I've discussed it ad nauseum in several places But, if you're using a fast cast defense to avoid an attack, no you shouldn't add concentration check on top of it. The penalty for fast casting is -10 to the casting roll, whether it's a mastered formulaic with the fast casting ability or a spontaneous fast cast, you're almost guaranteed to lose a fatigue level unless it's a spell in your Form specialty, have stalwart mastery (limited to Mercere, Cult of Mercere and related groups) or you get fairly lucky on the die roll. Requiring a concentration roll, IMO, is a double penalty. That's something i try and avoid doing to players. One house rule in two sagas I've been in, is to require all spells in a round be fast cast, if you use fast casting. IMO, this is the most fair ruling, and requires players invest time and XP into fast casting mastery for their defense and offense spells.

IMO, Rotgiers is not a combat magus, he's a magus designed to perform well in the Tournament.

Regarding your example, and dodging, I would instead have the character learn Wizard's Leap, master it for fast casting, the cost is two seasons of time, and it's going to be more effective. Dodging is a desperation attempt to avoid damage when all other options have failed (the finesse roll for timing the leap to happen before the attack) and is generally unlikely to work. And yea, I don't think it's a bug of the system, if mundanes get the drop on magi, without their defenses, it's very possible to take them down. Magi are nearly unstoppable if prepared, I mean that's why they take meat shields, because they know they're going to get attacked, and they need the grogs to hold off the whats-it while they bring their magic to bear to solve the problem. If the whats-it happens to get lucky and takes out the shield grog, and no one else can get to the magus before the next round to protect him, yeah, it should have a chance of going very badly. If a magus in an Ars Magica story goes down, and he's the only magus in the story, I've seen TPKs or nearly TPKs where a companion or grog comes back the covenant horribly maimed to tell the story...

One could argue that keeping focus for casting a spell while moving around is harder if you are also wounded. But perhaps too harsh overall. But that seems to be RAW.

I can find arguments to not apply Wound Penalties, because if several situations apply - Like dodging but failing so you get hit - you'd only roll for the higher one and that is likely for being injured which is for highest Ease Factor anyway. The accumulated penalty for many wounds is not a factor but that would be crushing.
This way it is the immediate shock which makes spellcasting harder not the continued pain and debilitating effects of wounds.

Another fix is to simply lower ease factors by 3 but apply Wound Penalties. This makes things a bit easier if you only get a Light wound but for Heavy Wounds the situation is worse than not applying penalties but keeping the ease factors as they are.

I find it best to not require Concentration rolls for fast cast defense. As a quicker spell it must require less concentration.

Using Silver Cord as a bonus makes sense in a way. Not 100% to me since Silver Cord is abut mental effects and although Concentration is about strength of will is resistance to injury not physical thing? But Bronze Cord is already quite good. I should see how my Troupe feels about this. It is sort of a fix for a situation one player thought was harsh.

The silver cord is pretty weak, a boost for concentrating when casting spells is pretty the,Aric for familiars in literature.

Combat is dangerous, though. If one is going to engage in it, be prepared, whether that's having a shield grog or just a broad range of offensive and defensive spells. The combat section all but makes it explicit for magi to have shield grogs, what with the rules for defending...

Being jostled is also riding e.g. on a moving cart or palanquin ... or a steed that really knows what it's doing so you don't have to pay even the least attention to controlling it. It is not being bumped into so hard that you get knocked to the ground.

That said, I can easily see being jostled being slightly easier than actively dodging. Try, yourself, performing any kind of task requiring mental concentration while moving through a dense crowd and see if it's harder to keep on top of things if a) you just allow the crowd to bump into you or b) if you actively try to avoid having them bump into you. For me, a) is definitely a bit easier.

Personally, I find concentration by the RAW rolls hard, but not unrealistic.

From my perspective, spellcasting concentration requires about the same level of focus as playing a harmonica or a fiddle without mistakes.
You are in a relaxed environment? Easy, virtually automatic (as long as you know how to play).
Having someone bump into you or surprise you with a gunshot? A bit harder, but it can be done, particularly if you've trained for it. Keep at it for several rounds, however, and you are bound to make a mistake sooner or later.
Having been hit by a mace that broke two of your ribs in the past round, and actively hopping around so as to avoid the aforementioned mace smash your skull this time? Yes, it is going to be insanely hard to get every note just right.

As has been stated by other posters, there's a reason why magi almost always have a shield grog with them, and ideally more if the situation is dangerous.