Your bull rush attacks throw enemies off balance.
Prerequisites
Strength 13, base attack bonus +6, Improved Bull Rush, Power Attack.
Benefit
You receive a +2 bonus on checks made to bull rush a foe, which stacks with Improved Bull Rush.
In addition, you can bull rush opponents up to two sizes larger than yourself, and bull rushed opponents provoke attacks of opportunity from movement.
Normal
You can only bull rush creatures up to one size category larger than you, and creatures moved by bull rush do not provoke attacks of opportunity.