Baseball has not been berry, berry good to Geena Davis. In fact, the game is making her batty. ''I haven't played in months,'' says Davis, who took up the sport to portray a star catcher in 1992's A League of Their Own. ''Now, whenever some celebrity softball thing comes up, I think I have to come out and be the best they've ever seen or I'll ruin my image.'' And Davis, who'll show her swash as a pirate in December's Cutthroat Island, is even more worried about competition from, say, a Pittsburgh Pirate. ''I was invited to play an exhibition game in Florida with retired ballplayers,'' says Davis. ''I said, 'Are you mad?' I was afraid those guys would take my head off.'' Lucky for her it's almost football season.