Tracy the Gorilla was known to use a baseball bat on occasion. He did so to fend off a rock thrown at him and the other Ghostbusters by Delwin the Troll. At this time he changed his headgear from his trusty fedora to a baseball cap.
Another instance in which Tracy made use of the bat was to protect a borrowed Alien Spaceship from being hit by asteroids. At the conclusion of that particular mission, set in the year 2340, Tracy's bat was autographed by three grateful aliens: Zorgon, Nexor and an Unidentified Alien. The bat was given an honorably place and mounted on a wall next to a window at Ghost Command afterwards.