I'm having this issue with my model. Once I applied the rig the left side (models right) seems to be snagging on something yet it's a mirror of the right side. Does anyone know what could be causing this? I noticed by moving the other leg it changes the shape of the deformation as well.
do you use bone envelopes? if yes, then they might be overlapping, they seem sticking to the other ankle. you can set the envelope radius in the bones "deform" tab. if you are using vertexgroups additionally, see if thats causing the issue, by unchecking it. the left foot vertices might belong to a group called like the right ankles bone.