If you need to know just how passionate MLB fans about their division rivalries, ask the Cardinals fan in your life about Jason Heyward signing with the Cubs ... then immediately duck and apologize for rubbing it in.
And Cubs-Cardinals certainly isn't the only example. Take, for instance, the Dodgers and Giants. On Dec. 13, 1956, the Dodgers traded Jackie Robinson -- the 1947 Rookie of the Year, the 1949 NL MVP, the man who hit .311 liftime, stole home in the World Series and brought championship baseball to Brooklyn -- to the rival Giants.
Instead of reporting to his new team, Robinson decided he'd rather retire.
Despite how it might appear, Robinson's retirement had nothing to do with being traded to the Giants. In fact, he penned a sincere letter to Giants owner Horace Stoneham to inform him of the decision (you know it's sincere because he signed it "Sincerely"):
Robinson's trade was later voided after he announced his retirement in Look magazine and sent the subsequent letter to Stoneham, so as not to leave the guy hanging.
The gap between the trade and Robinson's announcement also begged a photo opportunity when news of the swap broke. So, Robinson, his wife Rachel and their son Jackie Jr. posed with a bunch of New York Giants swag in the above photograph, now a relic of an era that never was.