CNN  — 

No shots were fired at the Barclays Center during a disturbance that sent people, including tennis star Naomi Osaka, running in fear early Sunday, said the New York City Police Department.

“After investigating the incident at the Barclays Center this morning, we determined that no shots were fired,” the NYPD 78th Precinct, which serves the Park Slope section of Brooklyn, said in a tweet on Sunday.

An NYPD spokesman told CNN there was a “sound disturbance” at the indoor arena that people mistook for gunfire. Eighteen people suffered injuries, and nine were transported to area hospitals, according to an NYPD spokesperson.

The source of the sound is unclear, police said.

The disturbance followed a boxing match between Devonte Davis and Rolando Romero at the center, and comes as the nation remains on edge following recent mass shootings in Buffalo, New York, and Uvalde, Texas.

Osaka, who was at the event, said she was “petrified” when she saw the commotion.

“I was just in the Barclays center and suddenly I heard shouting and saw people running, then we were being yelled at that there was an active shooter and we had to huddle in a room and close the doors,” Osaka said on Twitter.

In a later statement, the four-time tennis grand slam champion said: “I was lucky enough to have a security guard with me and I cannot imagine having to navigate through that situation by yourself, let alone being a child and it not being a false alarm.”