I can't say I've ever understood it myself, but grown men beating each other up has a long and storied history, going back at least to ancient Sumeria.
Modern-day boxing began its rise to popularity in the late 17th century. The Boston Brawlers got their start in the dockyards around the middle of the 18th century, but in 1804 they moved to a gym of their own on the north side of Beacon Hill. There they benefited from the wagering dollars of the wealthy socialites living on the hill's south side, who enjoyed nothing more than watching poor people hitting each other in the face for their pleasure.
I expect if you impress them enough with your manly prowess they'll give you something in return. Perhaps a toaster. Or a black eye.