At least Tony Dungy believes so.
During a 2011 preseason edition of NBC's "Football Night in America," the former Indianapolis Colts coach pointed to a violent shot that Manning took against the Washington Redskins during the 2006 season as the origin of the quarterback's neck issues. Williams was the defensive coordinator of that Redskins team.
On the 2006 play, Manning released the ball just before Redskins defensive ends Andre Carter and Phillip Daniels converged upon him. While Carter came in around Manning's waist and brought him down to his knees, Daniels came in high, bending back the quarterback's head and neck and knocking off his helmet in the process.
"I'm yelling at the ref (Scott Green), 'Where's the flag! Where's the flag!,'" Dungy said, according to The Post. "And I don't yell much, but I did then. So I didn't notice Peyton calling timeout and being shaken up. Peyton came to the sideline and said to (then-backup) Jim Sorgi, 'Jim, start warming up.' As the timeout went on, he said to us, 'I can stay in, but we need to run the ball here.'"
Manning was noticeably shaken up on the play, laying on the turf for a few extra seconds and reaching for his right shoulder. After Manning picked himself up, he called a timeout, and Sorgi was seen warming up on the sideline.
As Dungy noted, Manning never left the game. The Colts ran the ball on the next play and ultimately kicked a field goal, heading into halftime trailing 14-13.
"Then we sort of forgot about it at halftime, and Peyton seemed fine," Dungy continued. "He lit it up in the second half. He was on fire (throwing for 244 yards and three touchdowns). But that's the year we started cutting back on his throws at practice. ... Now, as I look back on it, there's no doubt in my mind that this was the start of his neck problems."