The Athletics selected Castro's contract from Triple-A Nashville on Sunday.

Castro will join the Athletics for what's likely a temporary basis to provide an extra arm out of the bullpen after relievers Sean Doolittle and Ryan Madson were traded to the Nationals on Sunday. The Athletics did take back another bullpen arm in Blake Treinen back in the deal, so once Treinen joins the big club, Castro could be shipped back to Triple-A. Over 38 innings with Nashville this season, the 29-year-old has supplied a 3.32 ERA to go with an eye-popping 63 strikeouts.

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