An off-duty NYPD Sergeant was arrested for brawling with a fellow concertgoer at a Billy Joel show, authorities said.

Joseph Brennan, 30, was at Joel’s Aug. 7 performance at Madison Square Garden when he got into a fight with another man at some point during the show, cops said.

No one was seriously hurt during the fight. It’s unclear what sparked the altercation.

Brennan was arrested Wednesday and suspended without pay following an investigation by the department’s Internal Affairs Bureau, cops said.

He was charged with assault and harassment, according to police.

It is not immediately clear why it took three months for authorities to charge Brennan.