According to the federal code concerning the flag, it is a "conduct violation" and not disrespectful to kneel. But it is, according to the code, disrespectful to display the flag in a horizontal manner. Such a display is done at every NFL game.
This whole issue is silly. It was actually going away until Trump got on his racist soapbox in Alabama in an effort to appeal to his redneck base.
I've been to many NFL games. A lot of people are buying a beer, in the bathroom, getting food and/or tailgating while the anthem is played. Are all these folks disrespectful??