I would guess its an issue of flexability. Based on your description, the point of tightness sounds like the tendon. Which connects the inner thigh muscles with the pelvis. Focused stretching, i.e. splits/straddle splits/chinese splits/side stretches should help alleviate the issue. I had a similar problem, only with the lower part of the thigh (where it connects with the knee joint). If not, its a more serious issue, like a pulled muscle, aggravated ligament, etc.
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