From 1976 to 1990, he pitched 15 seasons for the San Francisco Giants and Houston Astros, earning two All-Star appearances as well as the 1981 NL Comeback Player of the Year award.

He gained notoriety with his 1988 remarks disparaging umpire Pam Postema, the National Organization for Women, and gay people.

Born in Akron, Ohio, his family moved to the Napa Valley when he was nine years old, where he attended Calistoga High School.

[1] In the September 1978 issue of Sport, Jay Stuller wrote an extraordinarily positive article on Knepper, entitled, "You Can't Compare Him To Koufax...Yet".

[2][3] When Knepper's career failed to reach that standard, critics would later refer to that article and say, "You Can't Compare Him to Koufax...Ever.

[4] Knepper welcomed the trade, perceiving the Astros' clubhouse as strongly spiritual, and calling the Bay Area “such a liberal, almost anti-Christian society.

In the 1981 National League Division Series against the Los Angeles Dodgers, he started Game 3 with the Astros needing just one victory to advance.

However, Knepper allowed three runs in five innings and Los Angeles won 6-1 before rallying to win the series a couple of days later.

[12] During a 1988 season that was one of the best of his career, Knepper disparaged Pam Postema, a female AAA umpire officiating a Major League spring training game, citing his Christian beliefs.