A ball striking device, such as a golf club, includes a head that includes a face having a ball striking surface configured for striking a ball and a body connected to the face and extending rearward from the face. A face member formed primarily of a metallic material forms the face, and a body member is connected to the face member and extends rearward from the face member to form at least a portion of the body. The body member is formed at least partially of a polymer material, and has a doped portion containing a doping material dispersed within the polymer material. The doping material may have a different density than the polymer material, such that the doped portion has a different density than the portions of the body member not containing the doping material. A co-molding method may be used to form the ball striking device.