He was involved in competitive fights, some of which were arranged while others were not. Dan Inosanto stated, "There's no doubt in my mind that if Bruce Lee had gone into pro boxing, he could easily have ranked in the top three in the lightweight division or junior-welterweight division".
Lee defeated three-time champion British boxer Gary Elms by way of knockout in the third round in the 1958 Hong Kong Inter-School amateur Boxing Championships by using Wing Chun traps and high/low-level straight punches.
The following year, Lee became a member of the "Tigers of Junction Street," and was involved in numerous gang-related street fights. "In one of his last encounters, while removing his jacket the fellow he was squaring off against sucker punched him and blackened his eye. Bruce flew into a rage and went after him, knocking him out, breaking his opponent's arm. The police were called as a result". The incident took place on a Hong Kong rooftop at 10 pm on Wednesday, 29 April 1959.
In 1962, Lee knocked out Uechi, a Japanese black belt Karateka, in 11 seconds in a 1962 Full-Contact match in Seattle. It was refereed by Jesse Glover. The incident took place in Seattle at a YMCA handball court. Taki Kamura says the battle lasted 10 seconds in contrary to Hart's statement. Ed Hart states "The karate man arrived in his gi (uniform), complete with black belt, while Bruce showed up in his street clothes and simply took off his shoes. The fight lasted exactly 11 seconds – I know because I was the time keeper – and Bruce had hit the guy something like 15 times and kicked him once. I thought he'd killed him".
In Oakland, California in 1964 at Chinatown, Lee had a controversial private match with Wong Jack Man, a direct student of Ma Kin Fung known for his mastery of Xingyiquan, Northern Shaolin, and Tai chi chuan. According to Lee, the Chinese community issued an ultimatum to him to stop teaching non-Chinese; when he refused to comply he was challenged to a combat match with Wong, the arrangement being that if Lee lost he would have to shut down his school while if he won then Lee would be free to teach Caucasians or anyone else. Wong denies this, stating that he requested to fight Lee after Lee issued an open challenge during one of Lee's demonstrations at a Chinatown theatre, and that Wong himself did not discriminate against Caucasians or other non-Chinese. Lee commented, "That paper had all the names of the sifu from Chinatown, but they don't scare me".
Individuals known to have witnessed the match included Cadwell, James Lee (Bruce Lee's associate, no relation) and William Chen, a teacher of Tai chi chuan. Wong and witness William Chen stated that the fight lasted an unusually long 20–25 minutes. According to Bruce Lee, Linda Lee Cadwell, and James Yimm Lee, the fight lasted 3 minutes with a decisive victory for Bruce. "The fight ensued, it was a no holds barred fight, it took three minutes. Bruce got this guy down to the ground and said 'do you give up?' and the man said he gave up". — Linda Lee Cadwell
Wong Jack Man published his own account of the battle in the Chinese Pacific Weekly, a Chinese-language newspaper in San Francisco, which contained another challenge to Lee for a public rematch. Lee had no reciprocation to Wong's article nor were there any further public announcements by either, but Lee had continued to teach Caucasians.
Lee's eventual celebrity put him in the path of a number of men who sought to make a name for themselves by causing a confrontation with Lee. A challenger had invaded Lee's private home in Hong Kong by trespassing into the backyard to incite Lee in combat. Lee finished the challenger violently with a kick, infuriated over the home invasion. Describing the incident, Herb Jackson states,
One time one fellow got over that wall, got into his yard and challenged him and he says 'how good are you?' And Bruce was poppin mad. He [Bruce] says 'he gets the idea, this guy, to come and invade my home, my own private home, invade it and challenge me.' He said he got so mad that he gave the hardest kick he ever gave anyone in his life.
Bob Wall, USPK karate champion and Lee's co-star in Enter the Dragon, recalled one encounter that transpired after a film extra kept taunting Lee. The extra yelled that Lee was "a movie star, not a martial artist," that he "wasn't much of a fighter". Lee answered his taunts by asking him to jump down from the wall he was sitting on. Wall described Lee's opponent as "a gang-banger type of guy from Hong Kong," a "damned good martial artist," and observed that he was fast, strong, and bigger than Bruce.
This kid was good. He was strong and fast, and he was really trying to punch Bruce's brains in. But Bruce just methodically took him apart. Bruce kept moving so well, this kid couldn't touch him...then all of a sudden, Bruce got him and rammed his ass with the wall and swept him up, proceeding to drop him and plant his knee into his opponent's chest, locked his arm out straight, and nailed him in the face repeatedly". — Bob Wall