June 15, 1964: Lou Brock, Cubs to Cardinals
This is one of the most lopsided deals of all time: The Cubs sent the Cardinals a three-player package including pitchers Jack Spring and Paul Toth and a speedy 25-year-old outfielder who to that point had hit .257/.306/.383 with 20 homers and 50 steals in parts of four seasons. In exchange Chicago got pitchers Ernie Broglio and Bobby Shantz and outfielder Doug Clemens. Toth never pitched in the majors again, Spring and Shantz combined for fewer than 15 innings over the remainders of their careers and Clemens was replacement level fodder. Broglio, a former 20-game winner and the key piece for the Cubs, famously went 7-19 with a 4.50 ERA over the next 2 1/2 seasons with Chicago.
Brock, on the other hand, hit .348/.387/.527 with St. Louis the rest of the way, finishing with 200 hits, 14 homers and 43 steals overall and keying them to a pennant before hitting .300 in a World Series win over the Yankees. He would go on to set the single-season and all-time records for stolen bases, become the 14th member of the 3,000 hit club and batting a sizzling .391/.424/.655 with four homers and 14 steals in three World Series. He was elected to the Hall of Fame in 1985, his first year of eligibility.