street fighter vs battler

street fighter and battler both are nouns.

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

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

street fighter: someone who learned to fight in the streets rather than being formally trained in the sport of boxing
battler: someone who fights (or is fighting)

Other hypernyms of street fighter include belligerent, combatant, fighter, scrapper.

street fighter (noun)	battler (noun)
a contestant who is very aggressive and willing to use underhand methods	someone who fights (or is fighting)
someone who learned to fight in the streets rather than being formally trained in the sport of boxing