street fighter vs contender

street fighter and contender both are nouns.

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

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

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

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

street fighter (noun)	contender (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