The 32-year-old was known as one of the most popular available relievers heading in to Wednesday's Trade Deadline, which is the only Trade Deadline of the season, making it even more important. Oakland gave the Royals outfielder Dairo Blanco and right-handed pitcher Ismaiel Aquino to complete the trade.
Diekman's ERA is a bit elevated at 4.75 on the season, although, he ranks 11th among relievers with 13.6 strikeouts per nine innings. He signed a one-year, $2.25 million contract with the Royals in the off-season, with a mutual option for the 2020 season, that now includes the Athletics.
He has traveled around a bit, playing for the Philadelphia Phillies, Texas Rangers, and Arizona Diamondbacks, posting a 3.87 ERA for his career. He joins an Athletics bullpen that holds a 3.94 ERA, which is good for seventh in the majors. They sit eight games behind the Houston Astros in the American League West Division, but are tied with the Boston Red Sox for third place in the American League Wild Card race, just a half game behind the Tampa Bay Rays.