There is a false rumor that has been spread around that supposedly states that players are supposed to stand at attention during the national anthem. Despite rumors and even people citing specific passages that o not exist there is actually nothing said about the national anthem in the NFL rulebook.
Some fans are saying that rules pertaining to the anthem can be found on pages A62 and A63 however a look at the rule book will show that there are actually not even pages for A62 or A63 within the covers of the NFL handbook. Page 62 deals with different fouls and page 63 continues onto more rules about fouls.