Panthers coach Ron Rivera said after the game that Newton committed "a travel dress code violation," adding that he made the decision to treat Newton "like I do all the other players on the team, and he didn't start."
Newton offered further explanation.
"I didn't follow dress code, and Coach told me I wasn't going to start. I stand by his decision," said Newton, who confirmed that the specific violation was that he was not wearing a tie on the team flight from San Jose, California, to Seattle on Saturday.
Newton, dressed postgame in the same black turtleneck under a coat that he wore on the flight, attributed the issue to "a lack of communication on my part. I have to be clearer moving forward on how certain things are done."
The Panthers had been in California for more than a week, having played in Oakland last Sunday. On Friday, players shipped most of the clothes they packed for the trip back to Charlotte, North Carolina.
Newton explained that after sending his clothes, he did not have a dress shirt and was unable to find one in his size by the time he realized he needed it.
He said that while he was offered a number of ties to wear, "I can't wear a tie with this," referring to his turtleneck.
"I felt like I wore a similar outfit to this before and nothing was said," added Newton, "but [Rivera] has rules in place, and I have to abide by them. No person is greater than the next person."
Yeah. Y'all are gonna have to explain that one to me ASAP— Stephen Curry (@StephenCurry30) December 5, 2016
The Panthers held the Seahawks to a field goal after Morgan's pick, and Newton took the field for Carolina's second series.
It was the second game this season the reigning NFL MVP had not started. He missed a Week 6 game against the Tampa Bay Buccaneers with a concussion.