10. Feb. 1, 1999: Yankees Dump Mike Lowell to Florida for Todd Noel, Mark Johnson and Ed Yarnall
At the time, the Yankees likely believed in Scott Brosius (smart, coming off 1998 and his World Series MVP campaign) and couldn't envision a role for Mike Lowell (short-sighted).
Instead of continuing to develop their 25-year-old infielder, they shipped Lowell to the Marlins, where he subconsciously vowed revenge. Unsurprisingly, the slugging third baseman went on to sting the Yankees not once, but twice.
In 2003 with Florida, he helped lead the charge to upset the Yanks in the World Series, hitting 32 homers during the regular season and ripping two more in a seven-game NLCS squeaker against the Cubs (though he only hit .217 in the Fall Classic).
And yes, in 2007, he went and got the Red Sox a second World Series in the era, hitting .333 with a homer in the ALCS and .400 with a bomb against the Rockies, earning WS MVP. Boston acquired Lowell in the wildly successful Hanley Ramirez trade that also sent Josh Beckett to Beantown. The Yankees? They turned him into Ed Yarnall.