When I was a kid in the mid 1970's, we used to attend the Univ. Michigan home football games. At the time, there was a "black student section," and most of those students didn't stand for the National Anthem. When I asked my mother why, she said that they were "protesting the war, I guess," which wasn't a particularly satisfying answer since the war was over and no one else was sitting for the Anthem. I didn't really think much about it again until recently with the Kaepernick controversy.
I recall in one of the more difficult times of my life turning to patriotism and proudly putting my hand over my heart as the Anthem played, although that wasn't that sustaining. It became difficult for me during the Iraq War, which I actively opposed, when sporting events were effectively being used for propaganda and felt like a turn from patriotism to nationalism, as did displaying a flag. I went to a few sporting events at the time and, rather than make a scene, snuck off to the concession stand during the Anthem. At the height of the War, I had moved to New Zealand and a friend there invited me to a Rugby match. I noticed that they didn't play their National Anthem before the match and he seemed amused when I asked about it, although he then begrudgingly admitted that when he was a kid, they used to stand up before a movie started and sing God Save the Queen.
I haven't been to a game in a long time, and I am not sure what I would do about the Anthem, but I think at this point, rising for the Anthem would only be a way to avoid creating a scene, as I don't really have positive associations with it, anymore.