Video of the boys & a question ?

His back end looks a bit odd to me, though I can't put my finger on why. I wouldn't say he looks lame on one specific leg though. There's a few moments when one hind or the other isn't extending or flexing freely - in particular, around 1:10-ish really caught my eye because that off-hind really isn't extending forwards the way it should. It looks like he's very stiff at the back.

The sand in your school looks a bit deep and I'd be interested to see him being trotted up in a straight line on a hard surface.
 
In the first video it seems as if his near side hind leg is stiff (the solid colour leg). He bucks and seems uncomfortable doing tight clockwise circles with the weight on it. His other leg (white sock) seems to extend and bend a lot more. Trotting in a straight line did not show it as much imo.
 
how old is he?

I struggled to really analyse properly from the video, but he looks quite unbalanced particularly on the lunge. He looks like he isn't bending and is going really quite quickly alot of the time?

Have you tried really slowing him down to build up some more muscle and balance?
 
He does the classic of bending himself out wards to compensate avoidance of the lung line Monty Roberts explians it better, but it gives him the impression of almost crossing his hind legs under himself have you tried longlining to see if he goes any differently.
 
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