It is you who are mistaken.  There actually is a law:
(b)Conduct During Playing.—During a rendition of the national anthem—
(1) when the flag is displayed—
. . . .
(C) all other persons present should face the flag and stand at attention with their right hand over the heart, and men not in uniform, if applicable, should remove their headdress with their right hand and hold it at the left shoulder, the hand being over the heart;  . . . . 36 U.S. Code § 301 

Players protesting by kneeling during the National Anthem are giving a big middle finger to anyone who loves our flag and our Country for which it is a symbol. The NFL Approves. Message heard; station changed; stands avoided.  

The players have a right to protest on the job if their employer approves, which clearly the NFL does.  I hate their message.  I support their right to convey it. I'll exercise my right to react to their message and will avoid providing any monetary support whatsoever to the NFL while this protest continues.