He didn't direct the film, or write the script.

He co-wrote the script. I have no idea. He probably wanted to be creative and stretch himself.

1) "Oh man, Forget Paris, one of his many awful movies. He has done some embarrassingly bad movies (Analyze That, My Giant , Fathers' Day, City Slickers II, Mr. Saturday Night) and in his best movie, City Slickers, he wears a Mets hat the whole film. As a Yankee fan, I'd jump off the Brooklyn Bridge before I'd wear a Mets hat. It's not like the hat was central to his character. He could have wore anything else. He defiantly had enough power to say no to the f'n Met hat. The IMdb message board claims Billy said on WFAN the Mets donated to one of his charity's so he wore the hat. So if Steinbrenner threw some money at him he'd wear a Yankee hat? He just wore the hat because the Mets were the toast of the town back then and the Yanks were garbage." Source and further information: http://weblogs.newsday.com/sports/watchdog/blog/2008/03/billy_crystal_helps_yes_set_ra.html 2) "So what have we got? We've got a die hard Yankee fan wearing a Mets hat in a film that the whole country sees. There are a few ways to defend Billy C. in his choice of hats, but let's consider the possibilities: 1. He was a fair weather fan as a kid, loved the Yankees when they were winning then loved the Mets when they became good. 2. The Mets were a better sell, more popular and, thus more relatable to movie audiences. Basically, Crystal was selling out his true passion for box office gross 3. B.C. is full of shit, never cared about baseball and was just trying to overcome his lack of height (just like Eric K. w/ the red hair thing) by pretending to be a huge baseball fan. All three of these defenses don't hold much for Bily C. Either Billy C. was a sellout, a fair weather fan, or a liar. Rough one." Source and further information: http://www.yankees2000.com/y2k/2005/11/seinfeld-city-slickers-and-schmoozer.html