Why does my baby like to bang her head on purpose?

To sooth himself: Head banging is a rhythmic movement that soothes the child. Replacing another rhythmic movement like beating on a toy drum, clapping with music, dancing, riding a rocking horse could help. Be sure the environment is safe, they outgrow it by time. There are a few exceptions of children with cerebral palsy, autism or Down syndrome which may last long.

Common: Head banging can be an amplification of early infant fussing.It peaks in preverbal years .I've never heard or seen a head banger with a real head injury. This likely caught on when he noticed it grabbed your attention.If you ignore it(don't lock eyes), watching him out of peripheral vision, for safety, it should fade over time.