Is anyone else wondering if both these new people are the same person? I just... get that impression. Completely baseless, you could call it a gut feeling.
Onto the actual question, just in case I'm wrong or someone else runs across it and cares about the answer. If the leg is not correct, the animal should not be doing high impact sports. Cutting, reining, barrels and gaming are all high impact Western disciplines. Showjumping, eventing, Prince Phillip mounted games [English gaming - tons of fun on a speedy pony, but really hard on a horse!], eq over fences and hunter over fences are all high impact English disciplines. Anything that puts a lot of stress on the leg. Dressage can be "high impact" too, in its own way, though is usually harder on the hind legs and back than the front legs. Campdrafting, polo, polocrosse... others I'm sure.
A leg with a flaw such as being "curved inwards" [implies knock-kneed] is weaker and far more prone to injury. I will accept a leg that is a little forward at the knee, but never back. Never knock-kneed or bow-legged, and never bench-kneed [that's offset knees, to anyone who doesn't know]. I ride English but I know well the stresses put on the leg in barrel racing with those quick tight turns at high speed.
Say it with me, people! Legs are vital. Without a good leg, it doesn't matter how good the rest of the horse is. You're going to break it down if you push it to excel in a high impact sport.