Ohshita joined the Japanese Professional Baseball League in 1946, playing for the Senators and hitting a record 20 home runs.

The following season (1947), the Senators changed their name to the Tokyo Flyers; Ohshita won the leading-hitter and home-run-king titles, and became a household name in Japan.

After the 1951 season Ohshita was traded to the Nishitetsu Lions, with whom he won the 1954 Pacific League MVP award[2] with an average of .321.

Ohshita's uniform number (3) was retired by the Lions, but he wore it again later as manager of the Tokyo Toei Flyers in 1968.

When managing the Flyers, Ohshita used no signs in games and his players had no curfew; when the team finished last in the Pacific League, he was fired by its owner after the season.