I actually have given "short rests" in the middle of battles before - it was a large fight featuring several street gangs (that the PCs were allied with) vs a very powerful Yakuza-inspired crime syndicate. Fight went on for several rounds, the PCs got beat up, and then another of their allies arrived - another gang they hadn't been able to find earlier. The arriving gang got intro music as they slow-walked in, the PCs got a moral boost/second wind in the form of a short rest, and the fight went on. Yes this entire thing was heavily inspired by High and Low (still streaming on Netflix AFAIK)
But yeah that's very much an exception xD