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.
The group eventually made their way outside to the sidewalk in front of the store. Terrell was playing peacemaker, according to a witness.
Unfortunately, the heckler who allegedly started the confrontation just minutes earlier inside the store took an unprovoked swing at Owens.
A mistake ... and the fight was on.
After sizing up the man, the 48-year-old Hall of Famer landed a looping right punch square to the guy's chin, sending him to the pavement.
A few seconds later, the man returned to his feet ... seemingly a lot less willing to fight.
As a player, Terrell was one of the greatest receivers in NFL history. But, even as he approaches 50, he's still in absolutely awesome physical condition.
With the situation under control, Owens walked to his Tesla and drove away. It's unclear if the alleged heckler went inside for an ice pack and Advil.
Police were not called to the scene.