If combat is broken off, the fleeing party must accept an attack without any return on his part, the attacker adding +2 on his die roll for hit probability, and the armor class of the fleeing party can not include a shield. (J. Eric Holmes on what would later become known as the Attack of Opportunity, Dungeons & Dragons, p.21)One of the common criticisms of OD&D is that the combat system isn't realistic, and the common rejoinder to that is that D&D combat is abstract.
That's a perfectly good reply, too, in my opinion, and it reflects D&D's roots in earlier games like Chainmail and other wargames. In those, pieces often represented units of 100 men or more, and the attack/damage resolution was necessarily an abstraction, due to the aggregate nature of the unit. D&D simply evolved from that perfectly adequate system by dividing 100 men by 100, giving us the abstractions of Armor Class and Hit Points.
Nonetheless, there is abstract and there is Abstract. We don't talk about Triangle units hitting Squares and knocking off three points from the Blue Column; it's swords and axes hitting goblins and manticores and knocking their h.p. down. And dividing up an aggregation to derive the individual suffers from the "average family" problem, where every household has 2.73 children. So even in the early days, there was some desire to add a little bit of verisimilitude to combat, as evinced by the quote above.
Of course, combat was never the sole activity in the game, nor even the central one, despite what some might say, so it makes sense that it be dealt with on a level that reflects how much time and effort it should occupy. But weighed against this is the reality that in combat, more than any part of the game except maybe traps, your character can go down due to a bad die roll, and that giving the players more fiddly bits to twiddle can give them a feeling of control and fairness even when their hero meets an untimely end.
I mention all of this because I like Armor Class and Hit Points for the abstractions they are, but for me, the right level of detail is a moving target, and I sometimes find myself wanting more. I'm not thrilled by how complicated the rules have become on that score, however. I prefer my tactical flash to be as simple as possible, but no simpler. Something like this is a good start; a collection of easy-to-state and easy-to-adjudicate rules. Although I don't agree with all of them, this kind of thinking seems more elegant than all of the cumulative bonuses and multiple attack feats of later editions. So I'll be asking about this kind of thing in the future, and offering some suggestions of my own from time to time. I hope you'll find them useful.