Modeling a human and I’m having some trouble with the poses. I notice when I am move the leg up and forward the top of the thigh becomes deformed and looks like its caving in. I don’t believe it a problem with the weights but it must be something.
You are only showing the weights for one bone. Check that those vertices are not assigned to other bones or, better, post the .blend for us to check.
Looks as expected to me. You have the weight on a low-poly model, where the transition from strength 1 to 0 happens between 2 vertices. Therefore the mesh is being stretched unnaturally before the subsurf is applied.
You will need to smooth the weights, preferably on the higher-poly model (weights on a low poly model always look a bit strange).