LogFAQs > #975680854

"For anyone looking for a real answer...
The NES game is an attempt at a direct port of the arcade game. The arcade game had tough looking boxers with over the top silly, cartoony graphics and gameplay. For example, flexing an oversized beefy arm when you win, and punching your opponent so hard he flies out of the ring and hits the ceiling.
In between rounds, the arcade game developers wanted to express that the boxers are getting beat up and are struggling.
What you see in the arcade version is an animation of the boxers' faces looking wrecked and on the verge of defeat. The assistant, in an attempt to tell the boxer to keep at it and get back into the ring, grabs the boxer by his clothes and attempts to pull him back into the fight in an overly dramatic cartoon animation. The only clothes the boxer is wearing is his shorts, so he's grabbing him by the waistband.
https://www.youtube.com/watch?v=p91GwjjsplE&t=320
(at 5m20s)
For the NES port, the developers has fewer colors, fewer frames, and smaller sprites to work with. The result is boxers with much less expressive faces, and assistants who remain much closer between the boxers' legs.
Reference: I just looked at the video clip of the arcade gameplay."

https://www.reddit.com/r/retrogaming/comments/zzkv28/so_whats_really_going_on_between_rounds_in_ring/