Deadspin discovered at some point between 2014 and now the NFL changed the rule about players standing during the anthem.
No one knows when the rule was changed and there was never any announcement on the rule change. Also even though the game day manual is only given out to owners and team officials it somehow got into the hands of Trump, who used it to instruct Jerry Jones to ban his players from protesting.
The 2014 policy reads that failure to be on the field by the start of the national anthem may “result in disciplinary action from the League office.” The version currently being promulgated by the NFL revises this to read “result in discipline, such as fines, suspensions, and/or the forfeiture of draft choice(s) for violation of the above, including first offenses.”
That’s a pretty big change for two reasons: They’ve added a lot of punishment, and they’ve removed the language that punishment would come from the league office. We don’t know when the change was made; its language did not appear on the web at all until two weeks ago, and questions sent to an NFL spokesperson have yet to be answered.
Essentially it gives the power to owners to do as they pleased and this is probably why Jerry Jones felt he could say what he did.
As you can see NFL hasn’t made any comment. You can see the changes made below.
Jones emphasized NFL game ops manual several times and then this: "You know who reminded me about the game ops policy? Donald Trump."
— Chris Mortensen (@mortreport) October 10, 2017