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I think you’re basically just feeling your TFL freak out as you put it into it’s shortened position. Think about it like this: you’ve been lacking hip internal rotation for a while now, right? Your TFL is a major internal rotator muscle, and it lives in that little “flexor wad” corner on the front-outside of your hip (in the pocket zone). So now, when you try to actively go into internal rotation (especially with the hip flexed), you’re putting that muscle into a shortened position that it hasn’t had to work in for a loooooong time.
The same kind of thing happens when you’re trying to learn something like an L-sit. Early on, the front of your thigh will cramp up and freak out because you’re putting your rec fem in a way shortened position that it usually doesn’t perform in. It’s just a matter of letting the muscle get used to working in the new shape.
Basically, if you keep working on it actively that feeling of cramping should improve with time. Just give it a little ball love when you’re done the active stuff to release the tension (you don’t have to be TOO aggressive) and chill it back out again.