Baseball

Spahn reached the major leagues in 1942 at the age of 20. He clashed with Braves manager Casey Stengel, who sent him back to the minors after Spahn refused to throw at Brooklyn Dodgers batter Pee Wee Reese in an exhibition game.

Stengel later said that it was the worst managing mistake he had ever made: "I said "no guts" to a kid who went on to become a war hero and one of the greatest lefthanded pitchers you ever saw. You can't say I don't miss 'em when I miss 'em".
The 1942 Braves finished next to last, and Stengel was fired the following year. Spahn was reunited with his first manager 23 years later, for the even more woeful last-place New York Mets, and—referring to Stengel's success with the 1949–60 New York Yankees—later quipped, "I'm probably the only guy who played for Casey before and after he was a genius."
from Wikipedia