How many letters does the top answer for “someone who fights with his fists for sport” have?

The most common answer is boxer (5 letters).

Crossword clue: someone who fights with his fists for sport

2 answers found in Letterora's clue database (Wikidata facts, Open Trivia DB, WordNet and Webster definitions — all licensed sources).

boxer 5 letters wn-def

someone who fights with his fists for sport

pugilist 8 letters wn-def

someone who fights with his fists for sport

fight with the fists 50% similar → fistfight