Mr. Selee was the manager of the Boston Beaneaters when Pee Wee McFly was a pitcher for the team. On September 1, 1897, Marty McFly shouts towards his relative, and distracts him, knocking him unconscious. Utilizing Doc's inventions and a fake mustache, Marty steps in for his relative, winning the game.
Diamond Jim Tannen told Pee Wee McFly to throw the game, so Pee Wee leaves Hill Valley in fear. Marty once again plays as his distant relative the next day, and Diamond Jim Tannen storms the field when he realizes that he is not throwing the game. However, Tannen is arrested by the police. In the scuffle, Doc's invention is damaged, and Marty can no longer pitch.
Just as it looks like the Beaneaters are going to lose the pennant, as they had in the original timeline, Pee Wee McFly returns to take his rightful place as pitcher and win the game.