So my players and I all come from years of playing Call of Cthulhu, which utilizes the BRP system. We've been playing Pathfinder (and d20 in general) for about a year now, and we love it. One thing that my players really miss from BRP, though, is active defenses. With the d20 system, all of your defenses are passive (they're a number that the opponent is trying to beat). In BRP, when someone hits you with an attack, you are allowed a "dodge roll." You basically just make a roll to see if you avoid the attack, at the cost of your attack action on your next turn.
My players really miss this. They say that actively trying to avoid attacks made them feel more immersed in combat. So I was thinking of giving it back to them in Pathfinder.
Here's what I've thought of:
When an opponent successfully hits you with a melee weapon attack, you can attempt to parry it. You'd make a single attack at your highest base attack bonus, and if your roll + modifiers is higher than the attacker's roll + modifier, you successfully parry the blow and negate the damage. If you choose to do this, however, you forfeit your standard action on the next round.
So what is wrong with this? How will this blow up in my face? I've only been playing for about a year, as I said, and I still haven't grasped all of the little nuances of this game. If you see some gaping, terrifying hole in this home brew rule, please point it out to me.
Thanks!