Got your Back

[Knightfall]

Most of that is good, but for the Benefit part, I would suggest something like:
Benefit: Whenever an opponent that you threaten attempts an attack of opportunity against one of your allies, you may immediately make an attack of opportunity against that opponent. If your attack of opportunity would hit your opponent, you have the option of inflicting normal damage against the opponent or causing no damage but instead interrupting their attack of opportunity and preventing them from making their attack of opportunity against your ally.

Excellent Benefit description, very concise. Thanks for your input.

 

[Machiavelli]

That's perfect. It allows you a chance to just kill the malicious foe outright, if you think you are able to before he lands his blow, or to block his AoO chance directly at the cost of leaving him more HP that you will have to wear your way through next turn. Either way, your ally doesn't get hit. You've "got his back".

 

[gamecat]

Hm. I like it!