Feat Boost: Beatdown (Improved Combat Maneuver [Trip])
Source
Character Operations Manual pg. 88
Whenever a prone opponent that you threaten attempts to stand up from prone, as a reaction you can make a melee attack against that opponent. This functions similarly to an attack of opportunity, except your attack resolves before the opponent’s action (meaning they’re still prone when your attack roll and damage are resolved). You cannot use this attack to make a combat maneuver, even if you have another ability or item that would normally allow you to do so.
Dragonscript
ID
64f5664722756a16df9ccd3d