Just looked at a couple of my shots in Snapdragon. 70 yards wide with enough space in the corners to not be too bothersome. Players and fans prefer another 5 yards width. Galaxy’s home was built to go 80 or more, though they don’t draw it that wide these days.
I will mention Autzen in Eugene because there was an international exhibition in there a few years ago. They said it was 70 yards, it looked 68, and if it wasn’t preseason for the clubs involved, the touchlines would be a bit dangerous for being close to the walls. Part of the beauty of Autzen is how closed in it looks and feels for football games, which is why I don’t always advocate sharing. However, Snapdragon seems like the pitch of the stands is a wee bit steeper than Autzen (and has an upper deck), which helps the atmosphere, so this is something that can be done when engineered well.
By the way, San Diego does it with grass.