TAMPA -- Singer Chris Brown performed in front of a crowd of thousands Sunday night at Amalie Arena, but while that concert went on without incident, police are investigating what is alleged to have happened during Brown's paid appearance at AJA Channelside.

Tampa police say they're investigating an accusation of assault against the R&B singer, which happened after 1:00 a.m. Monday.

AJA Channelside photographer Bennie L. Vines said that Brown "sucker punched" him during an after party which Brown was paid to attend.

TPD said that Brown and his entourage arrived at the lounge and that is when Brown allegedly punched Vines for taking pictures of him.

Vines received a bloodied lip and he called TPD to report the alleged battery. By the time authorities arrived, Brown and his entourage had left AJA.

Vines refused medical treatment at the scene but he intends to press charges against Brown, TPD said.

A report from TMZ contains a YouTube video by user Wallace Pinho of the alleged altercation. In the video, a man in a yellow sweatshirt and purportedly Brown's bodyguard appears to be confronting the victim, Vines, in an offstage area next to a DJ booth. Brown, in a red sweatshirt and a hat is seen lunging at the victim and appearing to throw a punch.

The TMZ report also contains photos of Vines' bloodied lip.

Stay with 10News for more from this developing story.