Jacob Tanner Diekman (born January 21, 1987), is an American professional baseball pitcher for the Oakland Athletics of Major League Baseball (MLB).
He has previously played in MLB for the Philadelphia Phillies, Texas Rangers, Arizona Diamondbacks, and Kansas City Royals.
With the Phillies, Diekman began as a starting pitcher and progressed through a few levels of the Phillies' farm system in his first two years in that role, before adjusting his mechanics and lowering his arm slot to throw sidearm out of the bullpen, as a relief pitcher.
The adjustment worked and helped him move through the remaining levels of the Phillies' farm system.
In 2012, Diekman made his major league debut.
Over the next two seasons, he split time between the major league Phillies and their Triple-A (AAA) affiliate, the Lehigh Valley IronPigs, though while he was with the major league team, he was considered one of the "lone bright spots" in both 2012 and 2013.
Diekman throws a fastball in the upper-90s (mph), a slider, and an occasional changeup; his fastball is among the fastest of any left-handed reliever in the major leagues.