Bruno said he generally likes Young more than Harrison because Young is more approachable on court. But he said that he witnessed “ridiculous, immature behavior” from both players.

The incident occurred during a changeover at 4-3 in the first set Monday night. The players got into an argument that quickly grew so heated that the umpire had to come down from his chair to separate the players. Young, who is black, told ATP officials that the remark was made by Harrison, who is white, during that changeover.

The post on Young’s Twitter account read, “I’m shocked and disappointed, Ryan Harrison, to hear you tell me how you really feel about me as a black tennis player in the middle of our NY match.”

During its investigation, the ATP interviewed the umpire and the ball people and reviewed video of the incident, which shows Bruno standing behind Harrison. Audio of the exchange is unclear, but Bruno, who can be seen on the video drinking from a bottle of water and smirking, said he smiled because he thought the players were joking at first.

Harrison, he said, told Young not to audibly celebrate Harrison’s mistakes on the court, something that is considered poor sportsmanship in tennis. Young told Harrison to shut up, using an expletive. Bruno also said that Young leveled an abusive, nonracial, term at Harrison and challenged him to a fight. Harrison responded by holding his hand out, mocking Young for being short.

“Donald Young said, ‘Let’s take this outside, let’s fight outside,’ ” Bruno said. “Ryan kept saying, ‘You’re this tall,’ and kept gesturing with his hand, ‘You’re this tall, you’re this tall.’ ”