There had been rumors that the Yankees were involved in trade talks about Callaspo, but Oakland swept in to acquire him before the Yankees could make a deal. The Angels will receive minor-league infielder Grant Green in return, per Danny Knobler of CBS Sports.
Callaspo, 30, has a batting line of .252/.323/.348 in 2013. He can play multiple infield spots, and will fit in well with a versatile Athletics roster.
Callaspo will play second base for Oakland (per Jane Lee of MLB.com), which means he will replace Eric Sogard as the team's second baseman. Sogard is batting .268/.333/.377 this season for Oakland, and Callaspo is considered to be a better defensive option as well as a comparable offensive one.
Green, 25, was once a highly-touted college prospect who is hitting .325/.379/.500 for Sacramento in the hitter-happy Pacific Coast League.