William Mark Tosheff (June 2, 1926 – October 1, 2011) was an American professional basketball player.
A 6'1" guard, Tosheff played at Indiana University from 1947 to 1951 after a stint with the U.S. Army Air Corps. From 1951 to 1954, he played in the NBA as a member of the Indianapolis Olympians and Milwaukee Hawks, averaging 9.2 points in 203 games. Some sources list him as the 1952 NBA Co-Rookie of the Year (with Mel Hutchins); however, official NBA guides generally have not included pre-1953 winners.
In 1988, Tosheff founded the Pre-1965 NBA Players Association in order to secure fair pension plans for NBA players who were active before 1965. Tosheff lobbied to close a loophole in the NBA pension that granted benefits to post-1965 players with a minimum of three years of service, but required pre-1965 players have five years of service.
A San Diego resident, Tosheff died in Hawaii from cancer aged 85 on October 1, 2011.