Terrell Owens knocked out a man outside a CVS in Los Angeles after the guy allegedly harassed people in the store ... and TMZ Sports has obtained video of the fight captured by a witness.
The incident went down Saturday night around 11:30 PM at the pharmacy in Inglewood, CA.
Owens tells us he intended to quickly stop by the store and grab a few necessities. While inside, T.O. says a 49ers fan approached him and they had a friendly conversation. That's when things took a turn.
Terrell says a second man -- the guy who was ultimately clocked -- started talking crap to the fan Owens was conversing with. The aggressor threatened to beat up the men outside, according to witnesses.