Good comments. Let me ask more about one item: "combat momentum". I believe this is the same as what many term "initiative" – not in the game sense of "who hits first in the fight?", but in the sense of "having initiative", and "keeping" it, and eventually "losing" it, at which point the other guy "gains initiative" and starts attacking you.

It's often described just as you say: once you have it, you keep attacking it until the other guy gets it. Yet, like combat lulls, this real-life factor seems very difficult to bring off in game rules.

The difficulty is that there's no in-game explanation for why the defensive side can't counterattack freely. If the GM says "it's because you don't have combat momentum", how does he answer the player who responds with "I just attack. I can choose to do that if I really want to!"?

(That suggests to me a possible game solution if "combat momentum" rules are in place: Yes, the defending side can forcibly re-take the initiative by launching an attack, but at a steep -4 TH penalty. He'll probably need to use AOA at +4 to offset the -4, which means no defense, which possibly realistically reflects the danger of stepping into the other guy's momentum. How would you rate that idea?)

Anyway, putting aside game rules, what I'd like to ask is this: Is it possible to dissect the real-life mechanism of "combat momentum"? Is it purely a matter of mental readiness? Or is there a physical factor as well? Like this:

Say A attacks and B defends. After that, each naturally wants to be the next to attack. (This is RL, so no "turns"; either side could theoretically now launch an attack.) Now, if an attack from either A or B would take the same amount of time, then it's just as reasonable for B to strike next as for A; it's hard to see (from this alone) a physical explanation for A's continued "momentum".

On the other hand, if A's next attack (coming off a previous attack) is intrinsically faster than B's next attack (coming off of a defense, so requiring some change in stance), then that would offer a physical explanation for A's continued "momentum". Until something happens to change the timing (such as A hesitates or fumbles, etc.), it makes sense that A would keep launching attacks at a pace that keeps B on the defensive.

That's simplifying things a lot, of course, but I would be interested in hearing your thoughts on what specific physical or mental factors create "momentum".