Normal foot motion (both pronation and supination) is a function of hip rotation (referred to as Hip Drive).  Internal hip rotation pronates the ipsilateral foot, external hip rotation supinates the ipsilateral foot (See Model Left).   Xrays Foot - Internal and External Leg Rotation (Hip Drive), Pronating and Supinating the Foot respectively 

Abnormal foot motion: (1) Foot pronation occurring when the ipsilateral hip is externally rotating, (2) Foot supination occurring when the ipsilateral hip is internally rotating.

Ipsilateral = Same Side

Hip Drive - Pronation and Supination of the foot, driven by the internal - external rotations of the pelvis

Xrays of the Foot demonstrating Hip Drive