I personally think the NFL should take pot off the banned list, but until they do players that use it are taking a huge risk, even if they live in a state that legalized it.
UCLA had a kid awhile back who showed up as a freshman basketball player and per rumor had a medical marijuana card(before California legalized it for recreation). He was then notified by then coach Ben Howland that he didn't care if the card made it legal for him, it violated team rules. The 2 clashed over this and other things until the kid transferred away. His family was fairly vocal that they raised their kids to speak their minds and it was pretty clear that the kid considered part of that to be if I have a card, I should be able to use pot. Now why a 19 year old college freshman could get a MM card was a whole other story.
When you're talking NFL it's even a whole other story you're not just putting a scholarship at risk you're putting millions of dollars at risk.