[1] He attended the University of Southern California, where he played both sports, standing 6 feet 1 inch (1.85 m) tall and weighing 202 pounds (92 kg) during his active career.

A switch-hitting outfielder who threw right-handed, Johnston signed with the Pirates in 1959 and spent five full seasons in Pittsburgh's minor league system before making the Bucs' varsity out of spring training in 1964.

[2] His baseball career continued at the Triple-A level through 1966, and he batted .266 with 59 home runs in 938 minor league games.

In 1960, when he was struggling as a baseball player at the Class C level in the Pirates' system, he was invited to try out for the NFL Steelers.

According to the Pittsburgh Post-Gazette, Johnston called Branch Rickey, Jr., the Pirates' farm system director, seeking permission to play pro football as well as baseball.