July 31, 1993: Rickey Henderson, A's to Blue Jays
The A's had already done the nearly-unthinkable by trading away native son Henderson once—to the Yankees, in December 1984—then brought him back in June of '89, in time to help them win that year's World Series over the Giants and another pennant in '90, the year Henderson won the AL MVP award. He broke Brock's all-time stolen base record in 1991 and fueled another division title in '92, but the A's lost to the Blue Jays, who went on to win their first World Series.
With Oakland slipping into wretchedness in 1993 (they would lose 94 games) and the speedster's free agency looming, Oakland dealt Henderson to Toronto for righty reliever Steve Karsay and a player to be named later (outfielder Jose Herrerra). Henderson hit just .215/.356/.319 after being acquired, and he scuffled in the postseason as well, but he ignited the ninth inning rally in Game 6 that was capped by Joe Carter's title-winning homer against Phillies reliever Mitch Williams. Less than two months after the champagne flowed, he returned to the A's yet again as a free agent, and he would have a fourth stint with them again before his career ended in 2003. He was a first-ballot inductee to the Hall of Fame in 2009.