Shia LaBeouf wound up in police custody early Tuesday morning after a Mardi Gras brawl … and now we have all the gritty details behind the arrest.

The New Orleans Police Department tells TMZ … Shia was allegedly getting way too rowdy at a bar in the French Quarter. A staff member got Shia to leave … but the actor allegedly began pummeling the staffer with a closed fist as soon as they got outside.

Alleged victims say Shia finally left, but then came back … and this time he was even more aggressive, according to the police report.

Police say it took multiple people to hold Shia down, and when they let him up, police say Shia went after the same worker from earlier, striking that person in the upper body … then allegedly punched another person in the nose.

Police say Shia was taken to a hospital to be treated for unknown injuries. He was arrested after his release from the hospital and charged with 2 counts of simple battery.

Shia is no stranger to controversy … he entered court-mandated rehab after a 2017 arrest in Savannah, Georgia, for public drunkenness and disorderly conduct.