Demetrus Mongoni is a softball player whose team faces Stan's CIA softball team in "A League of His Own".
When Stan is accused by Steve and Hayley of faking his softball accomplishments, he invites them to watch him in a game, intending to prove them wrong. However, his actions on the field prove that he has been lying, and is topped when Mongoni hits a ground ball to him that he loses in his pants.
Later, after learning not to be afraid of the ball, Stan gets himself put back in another game, where he faces Mongoni playing for a different team, as Klaus notes that he's a ringer who bounces around. He hits yet another ground ball to Stan who almost gets this one, until he's mauled by Ricky Raccoon and blamed for costing his team a complete shutout.