The league wanted to make sure his knee brace was covered up and out of sight, according to NFL.com. Griffin said afterwards he wasn't sure why the NFL was so concerned about the brace, but did as he was told, per the story:
"Everybody in the league kept calling down to our sideline saying that I didn't cover the brace up," Griffin said after the 33-27 home loss to the Philadelphia Eagles. "I don't understand that one, but that's why we had to continue to do some stuff to cover the brace up with my sock."
This isn't the first time Griffin has had to deal with the league's version of the fashion police. Earlier this year in the preseason, Griffin wore a shirt with the words "Operation Patience" on it, earning him a $10,000 fine.
The reason for the NFL being so uptight about the knee brace still isn't clear, as no public comments to clarify have come down from Roger Goodell or anybody else for that matter.