Passive mobs not attacking

So I made a mob that attacks any player that attacks it. For the most part, it works. The mob walks up to the player when it is damaged. However, the mob doesn't execute the damage skill on the player:

Elephant:
Type: Horse
Display: '&7Elephant'
Health: 50
Damage: 10
Drops:
- Hide 2 0.5
LevelModifiers:
- health 5
- damage 0.5
Options:
HorseArmor: Iron
HorseColor: Gray
HorseSaddled: true
Tameable: True
HorseStyle: WHITEFIELD
MovementSpeed: 0.1...

Passive mobs not attacking