On arriving at Giants training camp, Emlen Tunnell, their defensive backfield coach, gave Carl the nickname Spider.

He was a Pro Bowl free safety in 1966, despite the Giants being the worst defensive team in points allowed/game in NFL history: 35.8 (14 games, see 1966 New York Giants season), the 1981 Baltimore Colts allowing 533 points in 16 games: 33.3; see List of National Football League records (team).

Lockhart also gained 328 yards returning punts and was famous for rarely calling for a fair catch.

In his honor, a "Spider patch" was worn by the Giants throughout their Super Bowl XXI-winning 1986 season.

Then living in Mahwah, New Jersey, Lockhart was not correctly diagnosed until he returned to see a doctor two years after his initial complaint.