Adrian Peterson Signs With Celebrity Boxing, Set To Fight Poker Rival In Ring

Adrian Peterson will be throwing hands against his poker rival again soon ... TMZ Sports has learned he's officially signed a contract to fight his adversary in a boxing ring!

The NFL legend put his John Hancock on a Celebrity Boxing contract Wednesday evening ... and after Joe "Baby Joe" Castaneda inked his deal with the fight org. earlier this week -- a sanctioned bout between the two is now incoming.

No official fight night date or location has been set yet -- but Celebrity Boxing founder Damon Feldman said in a video message he's getting to work on all that ASAP.

Peterson, meanwhile, told us in the hours after agreeing to the pact he's taking the bout seriously.

It will, of course, be the second time the former Vikings running back has squared off with Castaneda since May 27, when the two got into a violent altercation at a social club in Houston, Texas.

Some trash talk was what led to fists flying -- and while both guys sustained bloody wounds in the melee ... they've each said they don't have any bad blood toward one another.