49ers' Jauan Jennings Punched In Groin During 'MNF,' Retaliates After Game

12:34 PM PT -- The NFL just announced Tre'von Moehrig has been suspended one game without pay for "unsportsmanlike conduct."

Specifically, the league said Moehrig violated Rule 12, Section 3, Article 1 ... which addresses "any act which is contrary to the generally understood principles of sportsmanship" like "throwing a punch, or a forearm, or kicking at an opponent."

Like all punishments, Moehrig can appeal if he so wishes.

San Francisco 49ers receiver Jauan Jennings was on the receiving end of a punch to the junk during "Monday Night Football" ... and he was so pissed about the move, he ended up fighting back after the game.

The attack below the belt went down late in the Niners' 20-9 victory over the Carolina Panthers on primetime ... when Jennings and defensive back Tre'von Moehrig were in each other's faces amid the action.

Jennings was visibly frustrated and in pain over the act ... and after the win was secured, he retaliated by swinging on Moehrig.

Niners staffers and Panthers linebacker Krys Barnes did a great job of de-escalating the situation and separating the two ... and once they were in their respective locker rooms, they explained what happened from their points of view.

Moehrig said he acted in response to "dirty stuff" Jennings was doing during the matchup ... but the receiver seemed shocked by it all.

"It was just out of nowhere," Jennings -- who had five catches for 41 yards and a touchdown -- claimed. "It's probably just the history of me playing ball. I play hard. I'm physically stronger than a lot of DBs out there. A lot of things happen in between the whistle with me at least."

Expect consequences for both players ... as the league will likely fine -- and possibly suspend -- the athletes for their actions.

Even if the NFL takes issue with it, Jennings got support from his head coach, Kyle Shanahan ... who praised his guy for not "losing his mind" after getting hit "in the balls."