You interpose yourself between an attacker and your mount, defending your mount from harm.
Archetype
Feat type
Archetype Feat
Level
6
Traits
Archetype
Prerequisites
Cavalier Dedication
Trigger
An enemy makes a Strike or spell attack against your mount while you're riding it.
Actions
Reaction
You interpose yourself between an attacker and your mount, defending your mount from harm. Use your own defense against the triggering attack instead your mount's defense. If the triggering attack hits, you take the effects of the attack instead of your mount.
Source: Pathfinder Player Core 2, p. 193
Bring Defend Mount into a Pathfinder 2e game with The DM Screen.