I'm not disagreeing with any of that but simply stating that I can surmise what may have bee their motives for lack of action.But isn't it part of their job to protect people who are there, otherwise what is the point of them being there. For me if you ain't willing to at least help in some way when something like this happens then don't do the job.
If someone was kicking your head in, which looks like it was happening to one or two people when you look at the start of the video, I would expect the stewards to be helping in some way to stop it. How could you forgive yourself if you did just stand there and something serious happened to that person. I know I wouldn't be able to.