Head banging is a disorder commonly found in infants. Most common explanation to it is that it brings pleasure to the baby, as other activities such as thumb sucking. Another reason for it might be that it relieves tension and relaxes - indeed children often do it before they fall asleep.
Head banging might also be looked at as an expression of frustration in children. Infants, particularly those who still haven't discovered the proper ways to express feelings and emotions, often perform head banging in situations of discomfort.
The relaxation and stress motives described above remind of the drive and emotional scenery that usually push a compulsive skin picker to pick at skin.
Though the head banging disorder is usually attributed to children, it also occurs in adults, however in a different context. Head banging in adults describes a kind of dance, performed during listening to music, particularly rock and heavy metal music.
Though it is hard to see an underlying connection between head banging in children and the head banging "dance", one might find a relation between the two in that both activities involve movement, and bring pleasure to the person. This type of pleasure is sometimes called the kinesthetic drive - the joy in movement that all humans share.
Another interesting observation is the existence of a group of heavy rock music performers called "Skinpick Music". Note that oddly enough the name of this group is identical to the name of this website. One might only assume that the name implies compulsive skin picking.