In the late 19th century bare-knuckle fighting was a favorite sport of the working classes, in particular of the large immigrant Irish population. From Wikipedia:
Bare-knuckle boxing (also known as bare-knuckle,prizefighting, or fisticuffs) is the original form of boxing, closely related to ancient combat sports. It involves two individuals fighting without boxing gloves or other padding on their hands. The difference between a streetfight and a bare-knuckle boxing match is an accepted set of rules, such as not striking a downed opponent. … Boxing is a martial art and combat sport in which two people engage in a contest of strength, speed, reflexes, endurance and will, by throwing punches at each other, usually with gloved hands. Historically, the goals have been to weaken and knock down the opponent.
Boxing was closely associated with gambling and drinking; it was bloody and brutal, and for most of the 19th century, it was illegal. But it was still practiced openly and widely.
John L. Sullivan, one of the earliest prize fighters to attain national and international fame, opened a boxing arena and saloon in the Tenderloin, and made a great success of it. .