In the 13th Age roleplaying game, if you’re fighting an enemy with a sword, axe, spear or other melee weapon, according to the rules the two of you are engaged. (Congratulations!)*
If one of you wants to break off the fight and go somewhere else — whether to retreat, or to run over and help your buddy, or attack someone else — you have to roll a disengage check on a 20-sided die. A successful roll means you break off combat and move away with no penalty. A failed roll gives you two options. You can stay in combat (with no penalty), or you can disengage anyway, and your enemy gets a free swing at you. This, for those unfamiliar with roleplaying games, is called an “opportunity attack” or “attack of opportunity.”
On an RPGnet thread about 13th Age, someone who hadn’t yet seen the game said that opportunity attacks in the rules were a deal-breaker for him. This prompted someone else to ask how long this rule has been around in D&D. This sort of question puts me into Obsessive Researcher Mode.
I pulled out my Moldvay Basic and 1st edition Advanced Dungeons & Dragons books, and went hunting. Sure enough, early versions of opportunity attacks were there under different names.
In Moldvay D&D Basic (1981), page B25 describes two ways of breaking off engagement in melee combat. In a “fighting withdrawal” the defender can back up at half his movement rate without becoming vulnerable. A retreat allows the defender to move backward at more than 1/2 movement, but gives his opponent +2 to hit and the defender can’t make return attacks.
The 1st edition Dungeon Masters Guide (1979), page 70 says breaking off from melee “allows the opponent a free attack or attack routine. This attack is calculated as if it were a rear attack upon a stunned opponent. When this attack is completed, the retiring/fleeing party may move away at full movement rate, and unless the opponent pursues and is able to move at a higher rate of speed, the melee is ended and the situation becomes one of encounter avoidance.”
So opportunity attacks go back to at least 1e. If you own 0E or Holmes Basic, I’d love to know if it’s in there as well.
*That joke never gets old.