The rivalry between the Chicago White Sox and the Chicago Cubs is probably uglier in the stands than it is on the field. But it can get even uglier for fans who decide to switch sides.

Mike Grzyb, a former Cubs fans and current Sox fan, was profiled in a recent Crain’s Chicago Business article. Grzyb was as big a Cubs fan as they come, but a bet with a Sox-fan cousin sparked the switch in loyalty.

As the loser in the bet, Grzyb had to wear a Sox hat for a year and attend three Sox games at U.S. Cellular Field.

“I had fun,” Grzyb told Shia Kapos from Crain’s. “I spent less money tailgating (at Sox park) than I did hitting the bars in Wrigleyville.”

Now, Grzyb has since moved to the South Side and received plenty of criticism from friends and family, even his wife, who’s a Cubs fan. She was “like, ‘I don’t even know you anymore,’“ Grzyb recalls. “Now she’s used to it.”

But Grzyb isn’t the only person to have switched sides. Andrew McKenna was once a Sox fan and board chairman from 1975 to 1981, he stepped down when Jerry Reinsdorf purchased the team.

After leaving the Sox, McKenna was contacted by the Tribune Co., who had just purchased the Cubs. McKenna joined the North Siders in the same position he was with the Sox. McKenna left the Cubs’ organization in 1984.

“There was a little bit (of joking)” from his friends, McKenna told Kapos. But that just goes with the baseball climate in Chicago.

“I was definitely a Sox fan,” McKenna said. “But one of the great strengths of the city is that we have two major-league baseball teams. It creates a very energized atmosphere.”