Without justifying AT ALL the rider’s reaction (let me say that one more time, without justifying AT ALL THE RIDER’S REACTION)…
That horse looks like he plays real dirty. On the takeoff side she cantered up to what was going to be the right distance and he did a big prop like he was perhaps going to stop and spin out (or bolt-- a stride out it seems like he was going to pull SOMETHING and in response she put her leg on), then instead jumped big, and was ready to put his head down and porpoise on the landing. Looks like a horse that knows how to get you off on the takeoff or the landing and pulls both tricks out of his bag at shows when he knows he can.
THIS DOES NOT MEAN I THINK IT WAS APPROPRIATE TO KICK AT HIS BELLY OR YANK ON HIS MOUTH
But I get the feeling this horse is dirty, has done it before, maybe especially takes advantage of the show setting, and the rider may have lost her temper. This didn’t look like the first time she’d ridden to a fine distance on this horse at a show and got dumped in response.
THIS DOES NOT MEAN I THINK WHAT SHE DID WAS OKAY. It just means, I think that horse is one that can challenge your nerves. That’s all. I see a lot of people criticizing the RIDE and while I think the REACTION may have been unsportsmanlike, I think the ride reflects a dirty stopper and a horse that knows how to get a rider off in the show ring.