Here’s what the NFL game operations manual says regarding the national anthem:
"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."
Should, as defined by Merriam-Webster:—used in auxiliary function to express obligation, propriety, or expediency
May, as defined by Merriam-Webster: (
shall,
must)—used in law where the sense, purpose, or policy requires this interpretation
This doesn't even take into consideration the players own contracts, which I would believe contain clauses regarding Acceptable Conduct, and Conduct Detrimental to the Team.