Casting on the Defensive & AoOs

[paz]

In our last session, one of our players was missing, so I ran his character (a sorcerer) as well as my own. A rules query came up with his character's actions in combat that I hope someone can help with.

As the sorcerer, I tried to 'cast on the defensive' (as there was a foe adjacent) but failed on the concentration check. The GM ruled that because of this failure, the foe I was facing got an attack of opportunity against the sorcerer. Is this right, or is the mere act of 'casting on the defensive' enough to preclude any AoOs, even if the concentration check to cast the spell fails?

 

[el-remmen]

In our last session, one of our players was missing, so I ran his character (a sorcerer) as well as my own. A rules query came up with his character's actions in combat that I hope someone can help with.

As the sorcerer, I tried to 'cast on the defensive' (as there was a foe adjacent) but failed on the concentration check. The GM ruled that because of this failure, the foe I was facing got an attack of opportunity against the sorcerer. Is this right, or is the mere act of 'casting on the defensive' enough to preclude any AoOs, even if the concentration check to cast the spell fails?

From the SRD:

You can use Concentration to cast a spell, use a spell-like ability, or use a skill defensively, so as to avoid attacks of opportunity altogether. This doesn’t apply to other actions that might provoke attacks of opportunity.

The DC of the check is 15 (plus the spell’s level, if casting a spell or using a spell-like ability defensively). If the Concentration check succeeds, you may attempt the action normally without provoking any attacks of opportunity. If the Concentration check fails, the related action also automatically fails (with any appropriate ramifications), and the action is wasted, just as if your concentration had been disrupted by a distraction.

Emphasis is mine.

The answer is no, there is no AoO -the downside is only that the spell fails - and as an AoO is not a "appropriate ramifications" of a spell-failing - it does not happen.

 

[Hedgemage]

My group has houseruled it so that a failed concentration check does provoke an AoO and then the caster must make an additional check (against 15+damage taken) to get the spell off. This grew out of a misunderstanding of the rules originally, but when we discovered our mistake, everyone was willing to take the damage in exchange for the chance to still get the spell off.