In terms of the literal moments before attack commands go out, roleplay may be possible or even highly desirable in some circumstances but is wildly impractical in others, when merely getting the attack commands themselves fired off quickly enough can be tight timing. So as usual my opinion is that any hard requirement is not compatible with the combat system and the best option is to foster softer encouragement about roleplaying during less time constrained moments.
If you just wait until the other character tries to flee, you will very frequently lose your chance to attack at all and the fleeing tends to be a much greater hamper to the emoting, dialoging right then and there RP I think this thread is talking about.
As others said... RP does happen surrounding the attack. Your likely had RP character caught the attention of others. Maybe another player had RP where they paid your attacker or manipulated them so they wanted to attack your PC. Maybe the player of the attacker had a bunch of RP gathering information about your PC. Your PC will have the RP after the attack of dealing with it's fallout.
That's excluding the fact that, as Leech said, the punches and kicks and gunshots are RP in and of themselves. I fully agree with this. Often, I see players have their characters dialog and emote during the RP of the attack. Enriching it further. They don't have to do that and it can truly backfire on them when they do.
I'm not trying to entirely dismiss Leudo's suggestion though. I just don't think it's all about the dialog and posing done right before the 'attack' command is used. I think it extends out further. The fact is that the silent murder or noisy disfigurement with no message before or after is easier and quicker. They may be however, in my opinion, some of the least effective moves possible. At the same time I also know that the other, arguably more effective, options by necessity stretch things out and involve more effort.
I'd love to see more variety. More arguing and back and forth. More messaging and... More of it all. But I understand why people often take the simple and well used methods. I'll take them over nothing at all any day!
*BAM* "Remember that loan you took from Joe Baka?"
*BIFF* "Remember how you didn't pay it back?"
*POW* "He wants to know."
*SLAM* "Who."
*CRUNCH* "Raised you."
*SLAP* "To be so disrespectful."
That ish is fun af.