This is the +4 attack which can be made by a melee combatant against an enemy that breaks off of combat by moving more than 1“ in a round (see Avoiding. For this attack, the enemy counts as stunned and has no shield or DEX modifier. Thieves can backstab without checking HIS/MS. Bonuses from a parting attack do not stack with invisibility. Every combatant executing a parting attack on fleeing enemies gets only one attack routine as a parting attack, regardless of how many attack routines they normally get per round.
Times when a parting attack is NOT made are:
This is known as an “attack of opportunity” in later editions.