TMZ has learned ... the Miami Beach Police Department is now in the middle of a violent incident involving "American Idol" runner-up Adam Lambert ... after the alleged victim filed a police report.

Law enforcement sources tell us the paparazzo seen grappling with Lambert on the beach yesterday walked into a Miami Beach police station around 10:30 PM last night and filed a report ... accusing the singer of misdemeanor battery.

According to the police report, obtained by TMZ, the victim claims Adam grabbed his backpack "where the camera was placed" ... and "wrestled [the photog] to the ground forcefully."

One big problem -- in photos that were taken of the incident, the camera appears to be in the photog's hand ... not in his bag.

The police report also notes that the photog didn't sustain any "bruises or lacerations."

Cops tell detectives will decide if the case is worth turning over to the State's Attorney -- who will decide whether to prosecute Lambert. If convicted, Lambert could face up to one year in jail and a $1,000 fine.

After yesterday's clash -- Lambert went right to his Twitter account and posted, "I lost my temper for a sec but wow it felt great lol MIAMI!!!"