He signed with the Minnesota Vikings as an undrafted free agent in 1968. He played on the Vikings' taxi squad during the 1968 and 1969 seasons.[4] He signed with the Boston Patriots in 1970. He appeared in three games during the 1970 season.[1] He entered his first NFL game with two minutes and 18 seconds remaining and caught two passes, including a 22-yard touchdown reception.[4] He was cut by the Patriots in 1971 and returned to the Vikings' taxi squad that fall.[2]
Knief married Diane McClintock, and they had two son, Jason and Derek.[2][5] After retiring from football, he owned and operated a construction and real estate firm in Carroll, Iowa.[5] In 1997, he was inducted into the Morningside College M-Club Hall of Fame.[5]