Aggressive Block [free-action] (Feat 2)
Fighter
Trigger You use the Shield Block reaction, and the opponent that triggered Shield Block is adjacent to you and is your size or smaller.

You push back as you block the Attack, knocking your foe away or off balance. You use your Shield to push the triggering creature, either automatically Shoving it 5 feet or causing it to become Flat-Footed until the start of your next turn. The triggering creature chooses whether to be moved or become Flat-Footed. If it chooses to be moved, you choose the direction. If the Shove would cause it to hit a solid object, enter a square of difficult Terrain, or enter another creature’s space, it must become Flat-Footed instead of being moved.