Duncan played seven seasons with the San Diego Chargers, where he was a three-time AFL All-Star.

Duncan was a standout player at Druid High School in Tuscaloosa, Alabama.

[3] As a rookie with the Chargers in 1964, Duncan played just a little on defense at safety before becoming a starter at cornerback the following year in 1965 in place of an injured Dick Westmoreland.

[4] Playing in Washington under coach George Allen, Duncan became a nickelback, backing up Pat Fischer and Mike Bass, while also returning punts and kickoffs.

[2] After his playing career, Duncan returned to San Diego and dabbled in the restaurant business.