street fighter

A street fighter is someone who fights in unregulated, informal settings—back alleys, sidewalks, or anywhere outside organized venues.

The term suggests raw, scrappy combat without rules or referees: He learned to box in a gym but started as a street fighter.

Figuratively, it describes someone who competes aggressively and without polish in business or politics: She's a street fighter who clawed her way to the top. (Capitalized Street Fighter is the video game franchise.)