At the end of his first season of professional baseball, he suffering a torn rotator cuff in his right shoulder playing winter ball with the San Jose Bees.

Marshall appeared in one game as a pinch runner in 1967[2] before winning a job as a back up corner outfielder out of Spring training 1968.

[3] After a few pinch hitting appearances, Marshall went 3-for-5 with two runs scored and an RBI in his first start to lead the Giants to a 7-0 victory over the Atlanta Braves.

Marshall was dealt along with Ray Sadecki from the Giants to the New York Mets for Bob Heise and Jim Gosger on December 12, 1969.

[6] In his first at bat against his former franchise, Marshall hit a grand slam off Giants ace Gaylord Perry[7] on his way to a career high six home runs his first season as a Met.