Selznick, who was Jewish, was born in Los Angeles, California. He also lived in Canoga Park, California. Selznick attended Manual Arts High School in Los Angeles. He was a physical education major in college, and first began to play volleyball in 1949.
Volleyball teams that Selznick played on won seven U.S. Open Volleyball Championships: in 1951–53, 1956 (w/Hollywood YMCA), 1960, 1965 (w/Los Angeles’ Westside Jewish Community Center), and 1966 (w/Santa Monica Sand & Sea Club), and seven runner-up titles. He was the USA Volleyball (USVBA) MVP in 1959, 1960, and 1962.
He was an early supporter of California beach volleyball, and was designated the “First King of Beach Volleyball”. Selznick played with Ev Keller to win the 1950 State (CA) Beach Men’s Open. He later played with partner Don McMahon. He won every Laguna Beach Open from 1955 to 1961.
Selznick coached the US women's volleyball team, which won the gold medal at the 1963 Pan American Games and the 1964 Olympic Games. He also coached women’s teams that won six USVBA titles (1959–61, and 1963–65). His Nick’s Fish Market (L.A.) Women’s Team won national championships in 1978 and 1979.
At the 1996 Olympic Games in Atlanta, Selznick coached Sinjin Smith and Carl Henkel. In 2000, he coached Misty May and Holly McPeak, who qualified for the Olympic Games in Sydney, Australia.
The FIVB named Selznick one of the two top American players of the 20th century, with Karch Kiraly. The U.S. Volleyball Hall of Fame honored him as the Most Valuable Player of the 75th Anniversary Men’s 1953–77 All-Era Team, and the “All-Time Great Male Player”. In 1995, Volleyball magazine called him the "Karch Kiraly of his era."
- According to the State of California. California Birth Index, 1905-1995. Center for Health Statistics, California Department of Health Services, Sacramento, California. Searchable at http://www.familytreelegends.com/records/39461
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- United States Olympic Committee (1957). United States Olympic book. Retrieved August 18, 2011.