Police Commissioner Bill Bratton sited a “gangster lifestyle” on Thursday as contributing to the Irving Plaza shooting that killed a 33-year-old man and injured three others before a T.I. concert Wednesday night.  

Hundreds waited for the rapper to perform at the Union Square-area venue as the shooting started in a green room, which sits above the main stage and near a balcony where people were watching the show, at about 10 p.m., police said. Rappers Maino and Uncle Murda had just wrapped up their set, Chief of Detectives Robert Boyce said on Thursday.

T.I., who was headlining the show for about 950 fans, had not yet performed and was uninjured, Boyce added.

In the mayhem, Ronald McPhatter, 33, was fatally shot in the stomach, police said. He was taken to Mount Sinai Beth Israel where he was pronounced dead. 

A 26-year-old woman was also shot in the leg and a 34-year-old man shot in the chest. They were both taken to Bellevue Hospital Center in stable condition, police said.

Brooklyn rapper Troy Ave, whose real name is Roland Collins, 30, was shot in the leg. He got himself to NYU Medical Center, where investigators were talking to him, Boyce said. 

Boyce said police were “monitoring social media to see if this beef was instantaneous last night” or something that had been planned. While there had been no arrests as of Thursday, Boyce said there were “some very strong leads.”

Amid blood and overturned furniture, Boyce said investigators found five shell casings, and connected at least four of them to the same person. Metal detectors and security were present at the time, he said.

Speaking on The Len Berman and Todd Schnitt show on 710 WOR radio, Bratton said it wasn’t clear “whether it involved bodyguard, entourage, talent.”

“It’s unfortunate that still in that gangster rap world that’s what you’re dealing with,” he added.

On its Facebook page, Irving Plaza referred all inquiries to the NYPD.

“The safety of our guests is of the utmost importance,” the post reads.

With Lauren Cook.