Baker Mayfield has a target on his back for that whole flag-planting stunt -- and the Ohio State alums in the NFL will make him pay for it ... so says ex-Buckeyes star Beanie Wells.
The former OSU running back tells TMZ Sports Mayfield's move was "the ultimate disrespect ... a slap in the face" -- and current and former Ohio State players are pretty pissed about it.
Wells says he spoke with a bunch of current OSU players after they got beat by Oklahoma this weekend -- and they're embarassed.