Mob infighting

Mob infighting is a mechanic in Minecraft in which certain mobs retaliate against other mobs, as part of their mob AI.

If a mob capable of attacking is directly attacked by a player or another mob, the damaged mob stops attacking its current target and attacks the mob or player that damaged it. This causes the mob that did the damage to retaliate in turn, and the two of them become locked into a duel until one of them dies. This is useful in combat as it distracts two monsters temporarily, kills one of them, and severely weakens the other.

Once a mob has taken damage from a mob or player, that mob or player is set as the mob's permanent target. This means that even if another mob or player attacks an infighting mob, the infighting mob does not stop trying to attack its permanent target. A mob can refuse to infight with another monster if the player or a mob already attacked it, so the player or a mob was already set as the mob's permanent target. That mob does not infight with any other mob until the attacking player or mob dies. If the attacker goes beyond the mob's sight range, this resets the retaliating behavior and the mob either returns to neutral mode or searches for a new target.