Maas figured in one of the largest trades of the 1950s. In November 1957 the Tigers traded him with Bill Tuttle, Jim Small, John Tsitouris, Frank House, Kent Hadley, and Jim McManus to Kansas City for Billy Martin, Gus Zernial, Lou Skizas, Tom Morgan, Mickey McDermott, and Tim Thompson. The next year Maas went to the Yankees with Virgil Trucks for Bob Grim and Harry Simpson. In 1959, his best season, Maas was 14-8 with a 4.43 ERA and four saves, going 5-0 in relief.