Street Sweep

Combat

After driving your foe back, you can quickly knock it to the ground and slow it down.

Prerequisite: Str 15, Improved Bull Rush, Improved Unarmed Strike, Power Attack, Street Style†, base attack bonus +6 or monk level 5th.

Benefit: While using Street Style, the first time each round that you deal damage with an unarmed strike to a foe that you bull rushed with Street Style since the beginning of your last turn, that foe must succeed at a Fortitude save (DC = 10 + your base attack bonus) or be knocked prone and staggered for 1 round.

Source: Ultimate Intrigue