A prizefighter was a boxer who competed for money.
Prizefighters were still around as late as the 22nd century. Sven "Buttercup" Hansen was a notable prizefighter, and one of Seven of Nine's ancestors. (VOY: "11:59")
In 2375, Chakotay mistakenly believed he was involved in a prizefight while hallucinating. (VOY: "The Fight")