He's one of several Giants' prospects (along with Bobby Etheridge and Bob Schroeder) who couldn’t wrest a job away from the likes of Ken Henderson, Hal Lanier, Tito Fuentes, or an aging Jim Davenport.
Johnson joined the Giants' organization in 1961, and played in their farm system from 1961-67, at 3rd base and the outfield. He had a few games with the Giants during September call-ups in '66 and '67.
Frank was with the Giants for all of 1968. He played 67 games, often as a pinch-hitter or pinch-runner, but also started 30 games at 3rd base (mostly in May and June). He only hit .190 (with 7 RBI) that season, so guess where he was the next year?
Sunny Phoenix! After 7 games with the Giants during the 1st month of 1969, Johnson played 1B, 3B, and OF for the Giants' AAA team for the rest of the year. Not even a token September game with the big club.
Frank got a 2nd chance with the Giants in 1970, playing 67 games (again!). He made 24 starts in left field, backing up Henderson. This time he hit .273 with 31 RBI – much better than in 1968.
Johnson played 32 games during the first half of 1971, then was sent down to the minors for the rest of the season. Some guy named Dave Kingman took his place, and you know the rest.
Frank played in Japan in 1972, then back with the Giants' and Padres' AAA teams from 1973-75.