street fighter vs competitor

street fighter and competitor both are nouns.

Word	Noun	Adjective	Verb	Adverb
street fighter	Yes	No	No	No
competitor	Yes	No	No	No

As nouns, competitor is a hypernym of street fighter; that is, competitor is a word with a broader meaning than street fighter:

street fighter: a contestant who is very aggressive and willing to use underhand methods
competitor: the contestant you hope to defeat

Other hypernyms of street fighter include challenger, competition, contender, rival.

street fighter (noun)	competitor (noun)
a contestant who is very aggressive and willing to use underhand methods	the contestant you hope to defeat
someone who learned to fight in the streets rather than being formally trained in the sport of boxing