The LEGAL right, yes. Meaning the government cannot force anyone to stand for the national anthem by law.  And pretty much everyone is in agreement on that.

However, that's entirely different than an employer being able to make it a job requirement for their employees as part of the event their putting on.  And that employer being able to discipline those employees if they defy that job requirement.  They have just as much a right to do that, should they choose to exercise it.  

Just as the First Amendment allows fans/customers/citizens to speak out if they don't like the disrespect being shown by kneeling during the national anthem.  That's protected too.