From the previews it does look like Luke threw an elbow at the box, it seemed intentional, as it seemed he was quite aware she was there and seemed pissed about her crowding him. He was also guilty of blocking the box during that incident. It's nothing new, it happens, but the guy does not look like an innocent victim there. I honestly don't want to play the deaf card, but I give him the benefit of the doubt that he perhaps is used to being very animated or something instead of saying "get the heck off of me" because of his difficulties in communicating. He might not have realized at that instance how that movement was interpreted, but you could clearly hear her sister react verbally off camera to the elbow (if that wasn't a case of editing that is). He did, however, look quite agitated when they stepped away from the box, so he was worked up about something during that first incident. I'm wondering if she retaliated in some way for the elbow right then and there.
The second incident did seem as if she intended to block the box, perhaps in retaliation, likely angered from the first incident. He did not run into her intentionally, but on the heels of the elbow she likely believed he was being agressive. She called him a name, mommy didn't like it (of course), big daddy Phil will deal with it at the mat.
Perhaps there were other incidents between the two teams during that leg of the race that led up to the agression between them, however, both look wrong in some way. We will have to wait and see what it all truly was about.