Out of the four games he pitched for Oakland (two starts), Callahan's second outing was his best.

On June 27, 1983, he pitched six innings and gave up just one earned run in a 7–1 victory over the Kansas City Royals.

This took place in front of 21,841 fans at the Oakland–Alameda County Coliseum.

His final totals include a 1–2 record in 9.1 innings pitched, two strikeouts (Amos Otis and Billy Sample), and an earned run average of 12.54.

This biographical article relating to an American baseball pitcher born in the 1950s is a stub.