Florida Sheriff's Deputy Accidentally Shoots Partner With Taser, on Video

Viral video shows the moment a sheriff's deputy in Florida accidentally shot his partner in the back with a Taser ... and it looks painful.

The Jacksonville Sheriff's Office says deputies were trying to make an arrest following a Saturday night traffic stop when the suspect, Kheilan Haynes, started resisting.

Footage shows two deputies tussling with a man on the ground next to a Jeep when one of the deputies backs off, pulls out his Taser and fires ... hitting his partner in the backside, causing him to stiffen up and crumple to the ground as the suspect runs away.

According to the arrest report, obtained by TMZ, Sergeant T. Robinson says he was the one who Tasered his partner, Officer Z.J. Poole, by accident.

Robinson says his first shot hit Haynes, but the Taser had no apparent effect ... so he shot again ... and the probes missed and struck Poole. This time, the Taser worked.

Law enforcement says Haynes was resisting arrest and wouldn't remove his hands from under his body while on the ground ... prompting Robinson to whip out his Taser.

JSO says Haynes was stopped after being observed running a red light ... and they say deputies who responded to the scene ultimately tracked him down after he fled on foot and hit him with a Taser -- again -- incapacitating him.