Weakest portion of shoulder joint capsule is

(c) InferiorShoulder is weakest inferiorly but dislocates anteriorly because it is the direction of force that decides the dislocation but never the anatomical weakness for a particular joint, e.g. the force that causes anterior dislocation (Abduction and external rotation) is much more common as in throwing objects like ball or javelin as compared to force that causes inferior dislocation.