Baker Mayfield Headbutts Helmeted Teammates To Celebrate Panthers' Win

Baker Mayfield lost his mind -- and maybe even pieces of his forehead and scalp -- following the Panthers' win on Thursday ... headbutting his helmeted teammates -- repeatedly!!!

Carolina's backup QB performed the insane act just seconds before his squad officially beat the Falcons, 25-15, on "Thursday Night Football" ... and the move was so weird, even his own teammates appeared to be caught off guard.

Check out the footage from the game's broadcast -- you can see Baker, in nothing but a baseball cap, slamming his head into his teammates' over and over again as they came off the field.

Nearly every guy that he hit looked at him with a "what're you doing, bro" expression ... but Mayfield didn't seem to care.

Of course, the Panthers had only won one game since September prior to Thursday night -- and Baker's had a brutal year, getting hurt and then being benched in favor of P.J. Walker -- so maybe he didn't quite remember how to act following a victory?