Fox joined the NBA's Royals for the 1967–68 season. In 31 games for the Royals, he averaged 3.2 points and 3.1 rebounds in eight minutes per game. Then, on February 1, 1968, he was part of a big trade which sent him and Happy Hairston to the Detroit Pistons for Tom Van Arsdale and John Tresvant. His playing time increased to over 15 minutes per game in 24 games for the Pistons, and he averaged 4.1 points and 5.6 rebounds per game.