It comes down to a poor upbringing and education system.

Every nation has its own protocols and standards on their Flag and National Anthem. But Obama started this BS when videos of him showed up on Utube

not following protocol when the national anthem was played. He was a foreigner as far as I was concerned , by his behavior.

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4 U.S.C. United States Code, 2011 Edition. Title 4 - FLAG AND SEAL, SEAT OF GOVERNMENT, AND THE STATES CHAPTER 1 - THE FLAG §9. Conduct during hoisting, lowering or passing of flag. During the ceremony of hoisting or lowering the flag or when the flag is passing in a parade or in review, all persons present in uniform should render the military salute. Members of the Armed Forces and veterans who are present but not in uniform may render the military salute. All other persons present should face the flag and stand at attention with their right hand over the heart, or if applicable, remove their headdress with their right hand and hold it at the left shoulder, the hand being over the heart. Citizens of other countries present should stand at attention. All such conduct toward the flag in a moving column should be rendered at the moment the flag passes.
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The US education system is littered with liberal teachers and a snake pit of a teacher's union. Do U think they teach this anymore?
If these NFL players, or other Hollywood types don't like it, LEAVE! Go to another country, try to get a gig playing rugby or soccer... oh wait... those countries
have protocols too! Too bad !