Done waiting. Since you seem to be having trouble, let me help you out. Here's the rule from the NFL:
"The National Anthem MUST be played prior to every NFL game, and all players MUST be on the sideline for the National Anthem. During the National Anthem, players on the field and bench area SHOULD stand at attention, face the flag, hold helmets in their left hand, and refrain from talking. The home team SHOULD ensure that the American flag is in good condition. It SHOULD be pointed out to players and coaches that we continue to be judged by the public in this area of respect for the flag and our country. Failure to be on the field by the start of the National Anthem MAY result in discipline, such as fines, suspensions, and/or the forfeiture of draft choice(s) for violations of the above, including first offenses."
Notice how the language shifts between Must, Should, and May. It's subtle, yet critical for your understanding. Here is a good example of their use in another setting for you:
There is a world of difference between the three words however, the only real thing you can glean from the NFL rule is that they require the anthem to be played and the players to be on the sidelines. The "should" statements are suggestions but they are not requirements. Based on that, you can see that they suggest players stand but it's not a requirement. Finally, if players do not abide by the requirements and/or the suggestions, the NFL may fine/suspend them. The word "may" means they reserve the right to enforce the rules, or not. Therefore, if the NFL and/or the team owner have chosen to not enforce the rule you can conclude that it's not that important to them.