Oklahoma City star Russell Westbrook said he was verbally provoked, before directing a profanity-laced tirade at a fan during the Thunder's 98-89 win over the Utah Jazz on Tuesday (NZ time) in Salt Lake City.
A reporter from the Deseret News tweeted a video of Westbrook's comments to the fan.
"I promise you," Westbrook said to the fan. "You think I'm playing. I swear to God. I swear to God. I'll f**k you up, you and your wife. I'll f**k you up."
When another person appears to intervene, Westbrook says: "No, f**k that! F**k that!"
Then apparently addressing the fan again, he said: "I promise you, everything I love. Everything I love [n-word], I promise you."
On Wednesday (NZ time), the Jazz announced they'd issued a lifetime ban for the fan involved, Shane Kiesel, after "an investigation through video review and eyewitness accounts" of the incident.
Westbrook was hit with a $US25,000 ($NZ36,434) fine from the NBA for his part in the altercation.
After the game, Westbrook explained: "How it started was, a young man and his wife in the stands told me 'to get down on my knees like you used to'. To me, that's just completely disrespectful, to me, I think it's racial, and I think it's inappropriate and insensitive.
"If I had it to do over again, I would say the exact same thing. I truly will stand up for myself and my family.
"As for beating up his wife, I've never put my hand on a woman. I never will.
"Never been in any domestic violence before, but once he said the comment and his wife repeated the same thing as well, that's kind of how that started."
Salt Lake City NBC 5 identified the male fan involved and spoke with him.
Keisel said he was playfully bantering with Westbrook, before Westbrook started cursing at him.
"I never said a single swear word to him, not one," Keisel told the TV station.
"Initially, I was like, 'Oh, I'm talking with Westbrook, the guy is one of the greats. He's also classless...'
"He can threaten me all he wants. I was the one talking to him, but don't threaten a woman.
"She's 5 feet tall and 110 pounds, man. [She] never said a word to him."
Five fans at the game were issued 'warning cards', citing the NBA's code of conduct, after the incident, the Deseret News reported.
Last year, Westbrook knocked the cell phone out of the hand of a fan in Salt Lake City after a Thunder playoff loss.