A 6 ft 1 in (1.85 m), 215 lb (98 kg) right-handed pitcher, he appeared in 11 Major League Baseball games for the California Angels in 1969.
In his debut against the Cleveland Indians, he entered the game in relief of starting pitcher Steve Kealey in the third inning.
Geishert got Vern Fuller on a fly ball out, and went on to pitch four full innings of three-hit relief to earn the eventual 8–4 victory in his first MLB game.
On November 25, 1969, Geshert was included in a major interleague trade, going to the Cincinnati Reds with starting pitcher Jim McGlothlin and reliever Pedro Borbón for hard-hitting outfielder Alex Johnson and infielder Chico Ruiz.
On May 29, 1971, Geishert was again involved in a big trade, this time going to the San Francisco Giants along with infielder Frank Duffy for future star George Foster.