Rituals (and ceremonial castings) can easily take hours to perform and can be very elaborate. We ran into a situation in a recent session with a group of magi of... unknown friendliness casting a ritual. We could not tell who they were or whether they were friendly or not. As a result, we chose to simply observe rather than attempting to interfere. Would that be an auto-botch? Would it have been possible for the casters to pause and explain just what exactly was going on, or would interrupting the casting be an auto-botch?
Look at :
So, if your player magi had simply and firmly broken the Concentration of some of the casters, their spell would have failed - which could well have led to a botch, especially if much vis was involved. But they would not have caused an 'auto-botch' - meant as an unavoidable botch.
I would say that interrupting a ritual would require a concentration roll for the caster. I'd say the ease factor is 3 per magnitude of ritual (thumb rule, to avoid the easy to avoid danger but not automatically produce a botch).
Ritual magic is not very far from ring/circle magic and i remember something about botching the spell when interrupted drawing the circle.
It is rather:
(underscore mine) So breaking the ring is indeed not advisable, when sodales are drawing one in a ritual. There are less dangerous means to stop them, though.
Mmmm, still, interrupting another magus' ritual and forcing them to risk a Concentration roll could absolutely be considered a violation of the Code. In retrospect, we should have tried to get some kind of letter from our local Quaesitor before setting out to investigate...
It might also have helped, to quickly determine the Hermetic Form of the ritual (see ArM5 p.83), and to further analyze its purpose by considering its words and gestures (e. g. with an Int + Magic Theory, Artes Liberales or Philosophiae roll). And to decide about actions to take or not only afterwards.
Ah, yes, this was the source of my confusion. I mixed up rituals with the circle/ring casting. As for the ritual itself... it probably wouldn't have been illegal, except for the fact that a marched maga (who was invisible, and revealed herself only at the last second) and a demon (also incorporeal) were involved.