Kelley was designated for assignment by the Nationals following Tuesday's blowout win over the New York Mets. The reliever emphatically threw his glove on the mound and stared into his dugout after allowing a home run in the ninth inning.
Nationals general manager Mike Rizzo criticized Kelley for the outburst, calling the 34-year-old "selfish." Kelley later disagreed with the general manager's assessment.
Prior to his meltdown, Kelley had found a groove on the mound. Over his previous 21 appearances dating back to the beginning of June, he posted a 1.69 ERA with 20 strikeouts and only two walks in 21 1/3 innings.
Kelley becomes the second late-inning arm the Athletics have added over the last few weeks after also acquiring Jeurys Familia from the New York Mets in late July. To make room for Kelley on the roster, the A's moved outfielder Jake Smolinski to the 60-day disabled list.