After the 1961 season, Larsen was traded to the San Francisco Giants with Billy Pierce for Bob Farley, Eddie Fisher and Dom Zanni and a player to be named later (Verle Tiefenthaler). Larsen became a full-time relief pitcher, anchoring a strong bullpen that included Bobby Bolin and Stu Miller. He had five wins with 11 saves for the pennant-winning Giants. Larsen won the deciding game of the three-game playoff series against the Los Angeles Dodgers, relieving Juan Marichal in the eighth inning. In the 1962 World Series, Larsen won Game 4 pitching in relief, giving him a career World Series record of 4–2 with a 2.75 ERA. During his time with the Giants, Larsen earned the nickname of "Froggy" due to his hobby of hunting frogs and serving marinated frog legs to his Giants teammates.