Multiple news outlets identified the Jazz fan as Shane Keisel. Keisel told ESPN that he did not swear at Westbrook or otherwise say anything inappropriate, and that he believed they were having fun. In an interview with local television station KSL, Keisel said Westbrook had been using profanity and “acting a fool,” which fans responded to by heckling him.

Keisel said he saw Westbrook’s knees wrapped in towels, so he told him to “sit down and ice your knees, bro.” Westbrook responded that the wraps were for heat, Keisel said, adding that he then told Westbrook, “Well, you’re going to need it.” Keiser said the woman sitting next to him, who ESPN identified as his wife, Jennifer Huff, did not say anything to Westbrook and had her hands in her lap.

Attempts to reach Keisel on Tuesday were unsuccessful.

Keisel was sitting in the third row on the baseline, near the Thunder bench. Unlike in most other sports, in basketball fans can sit just a few feet away from players. This can lead to good-natured and spirited exchanges — like the back-and-forth heckling between Spike Lee and Reggie Miller in the 1990s — but also to large problems.

Most infamous is what is known as The Malice at the Palace in 2004. After a brawl between the Indiana Pacers and Detroit Pistons at The Palace of Auburn Hills in Detroit, a fan threw a drink at Ron Artest, a Pacers forward at the time who has since changed his name to Metta World Peace. Artest charged into the stands, followed closely by teammate Stephen Jackson, and threw a punch at a fan. Artest was suspended for 86 games, and five players eventually pleaded no contest to misdemeanor assault charges.

Since the incident, the N.B.A. has taken numerous steps to prevent violence, especially between players and fans. Players are now automatically suspended if they leave the bench during an on-court altercation, and fans whose unacceptable conduct is overheard by or reported to security are issued cards warning them that they can be ejected from the arena.

In a statement after the game, the Jazz said arena security issued several warning cards to fans during the game.

Westbrook has had a number of run-ins with fans in the past, including in Salt Lake City. During last year’s playoffs, Westbrook twice got into it with fans while leaving the court. The first time he stepped toward and yelled at a fan that was leaning over the railing talking to him; the second time Westbrook swiped at a phone that a fan had pushed toward his face.