Bam Margera recently found himself throwing down with a stranger -- a fist fight captured on camera, but Bam says he was simply protecting himself and friends ... TMZ has learned.

ICYMI ... the video shows the 'Jackass' star wailing on an unidentified man. The clip's making the rounds online and has many of Bam's fans speculating the face-off has something to do with a tattoo dispute Bam posted about Monday -- he's calling his latest ink job "highway robbery" -- but we're told this is an entirely separate incident.

Bam's manager Mike Quinn tells TMZ … the fight in question happened last week in L.A. -- and was sparked when the stranger threatened to kill Bam and his entourage outside of the property where Bam was staying.

Mike adds, "This individual, who had been pacing nearby for hours relentlessly, and causing disturbances by yelling and overturning trash cans, escalated the confrontation by punching Margera when he stepped outside to smoke."

We're told repeated calls to the police were made, but no assistance arrived. Mike says someone from Bam's camp began recording the incident in response to the aggressive harassment.

Bam tells us ... "I'm not going to be threatened or attacked without defending myself and my friends or people trying to just walk by this idiot, I aimed only to neutralize the threat and ensure the safety of my crew."

His rep tells TMZ the altercation ended swiftly with no injuries, and the aggressor eventually departed without returning.

This update comes a month after Bam was caught on camera getting into a heated argument with girlfriend Dannii Marie, who was concerned about his sobriety at the time.