Seventeen-year-old Brady Becker said he was simply trying to defend his friend when he intervened in an altercation with two other men — who turned out to be sheriff's deputies — at a Mardis Gras parade in Louisiana.
A bystander's cellphone captured video of the encounter, which took place Feb. 13 in Metairie, near New Orleans, WDSU reported.
Becker was left with a visible eye injury after the incident turned violent.
"I had no clue he was a cop," he said. "I thought this was some random guy, you know, waving his gun at everybody."
According to an arrest report, Becker and his friend were yelling "(expletive) the cops" when they were approached by the deputies.
Becker was booked on suspicion of possession of alcohol by a minor, resisting arrest, battery on a police officer and inciting a riot, according to the the Jefferson Parish Sheriff's Office.
The FBI's civil-rights division is investigating the incident.
Correction: An earlier version of this report misstated the area in which the incident occurred. The story has been updated to reflect the change.