Most casters of decent level can make the defensive casting check without a problem. So simply threatening them isn't enough, you have to put them in a situation where he can't cast. For humanoid casters grappling is clearly your best choice, IF you can afford to tie up the fighter and put him at the penalties that go along with grappling (there are many and some can be significant).
I'm not sure this works. If the caster 5' out of the threatened area he's not "moving within the threatened area", unless the text specifies otherwise.
blargney the second said:Thicket of Blades (any movement at all in your threatened area provokes an AoO. Devoted Spirit stance from Bo9S.) plus Evasive Reflexes (when someone provokes an AoO, you can instead immediately make a 5' step. Feat from Bo9S.) plus readied actions to whack 'em when they cast a spell. (especially lovely with standard action strikes that deal bonus damage)
equals spellcaster in a world of hurt. (priceless)
-blarg
I'm not sure this works. If the caster 5' out of the threatened area he's not "moving within the threatened area", unless the text specifies otherwise.