What's inside Sparkler's head?

It was a bit windy this morning. I didn't want to ride alone on the trail, so I decided to ride in the arena and spend the rest of the day doing barn/pasture chores.

Sparkler came into the arena curious as to what I was doing, so I saddled her up with her English saddle and sidepull and we took a spin. The first time around she was great and I was starting to think her problems were over. Then it began. Bang, she kicked out with her left rear leg. I told her to quit and made her go again. Bang, bang. Both rear legs kicked. So I backed her up and stopped for a while, then asked her to go forward. Kick, kick. We backed, tried forward and got more of the same. Now I'm really puzzled. This can't be her mouth - she has no bit with a sidepull. All indications are that this saddle fits. She shows no lameness. She is cycling quite hard, however.

Then Banjo walked through the tape I used to keep them out of the arena and Sparkler jogged down to the other end to meet him. He decided to go around and she followed him close behind, nice and smooth. He stopped and I tried to keep her moving. Kick, kick, no way.

Herd bound?

Is that what this is all about? It makes some sense. Weeks ago when all the horses but her were in the arena, she ran around outside and kicked the walls. Yesterday's ride was perfect because she was alongside Banjo. But what to do?

I decided to circle her if she kicked. She went ballistic. She tried to bite my boot, bite me, laid her ears back. Ok. I switched to backing her up every time she kicked, then just sitting. Every now and then we'd move a few yards, then she'd kick. She made it her goal to move close enough to the wall and kick it for effect. I wouldn't get off because that would mean she won. I tried circling her once more and again she laid her ears back and became vicious. I have never seen her vicious before which made me extremely sad.

At last, she made a half lap without a problem and I dismounted. She followed me on foot like a puppy as if to say she was sorry and gave me her pretty brown eyed look. How can you be mad?

I shoed her out and got on Banjo for about 15 minutes, working on slowing his walk and getting better stops. He's such a gem inside and outside.