I have a very strong recollection of watching this as a child.
The Ghostbusters get dragged into a game of Baseball played by the forces of Good and Evil. I think this was done in hell?
The plot hinges on the fact that the Evil side is free to cheat, but if the Good cheat they will lose the game. I think that Peter is tempted to cheat?
The episode in question was Night Game, and involved of all things an Indian burial ground.
Forces of good and evil:
an ancient Indian legend, "Once every 500 years, the supernatural forces of good and evil fight a battle. That battle always takes place on the same site." This site happened to be the very spot currently occupied by the Jaguars Stadium.
Evil Cheating:
the score was 0-0 in the eighth inning. Playing to their nature, the players for evil cheated and finally scored. The Ghostbusters tried to get the Umpire to penalize the players for evil for cheating. The Umpire contended that evil is allowed to cheat because that is the nature of evil.
Umpire: "I told you no one can be neutral. You had to choose. Would you cheat for your friend or would you trust in fair play and let good win on its own terms?"
Egon: No stop. We can't do it. If we cheat good loses!
Peter's involvement
While Egon thought about the Umpire, Winston revealed the soul that was at stake was Peter's. Peter fell to the ground and declared he was only going to Mets games.