According to the parent who shot the video at Weemes Elementary School in Los Angeles:

"This all started because my son's teacher was so unorganized. Basically because of budget issues all the kids had to share a cap and gown for pictures. One of the moms in the video was basically taking over and the other one didn't like it and told her something about it. The sad part was that there was an older lady that got pushed and she actually hit her head on a bookshelf and I rushed to help her but when this other mom rush to help us the angry women actually attacked the other mom."