Colts Hendricks began his pro football career as a second-round pick of the Baltimore Colts in the 1969 AFL-NFL Draft. He was initially listed as a defensive end, which is why he had the unusual number (for a linebacker) of 83. After coach Don Shula converted him to linebacker, he entered the starting lineup in the sixth game of his rookie 1969 season, the beginning of 69 consecutive starts with the Colts. He made 32 tackles and 2 sacks on the quarterback and knocked down 2 passes and blocked a field goal (the first of 25 blocked kicks in his career). He played a key role in the Colts' 1970 Super Bowl V-winning season. He was the starting strong-side linebacker and recorded 67 tackles and 1-1/2 sacks while intercepting a pass. He also recorded 2 blocked kicks and knocked down 5 passes. He and fellow linebackers Mike Curtis and Ray May anchored a unit that was one of the NFL's best in defending against the run; which was 102.8 yards per game – 6th in the NFL, and allowing only 2 rushing touchdowns all season (tied with the Los Angeles Rams for first in the NFL). They allowed only 234 points, 7th in the NFL. He was chosen to the first of four All-Pro selections in 1971. He had 63 tackles and picked off 5 passes while batting away 7 passes. He also recorded 5 sacks and blocked 2 more kicks. The Colts defense was ranked #1 in the NFL in fewest rushing yards allowed and lowest rushing attempt. The Colts made the playoffs but did not advance to the Super Bowl, losing to the Miami Dolphins. In 1972 Hendricks recorded 99 tackles, 6 sacks, knocked down 7 passes, intercepted two passes and blocked 2 field goals. The following season Hendricks made 86 tackles and 4 sacks (bringing his Colt total to 18-1/2) and picked off 3 passes (making his Colt total 11) for 33 yards, while batting away 7 passes for the third consecutive season and blocking a punt. He was second-team All-Pro in both 1972 and 1973. He played the last of five seasons with the Colts without signing a contract. Green Bay Packers One week after signing to begin play in 1975 with the World Football League's Jacksonville Sharks, Hendricks was traded along with a 1975 second-round pick (28th overall–traded to Los Angeles Rams for John Hadl)