The practice of scalping is notoriously associated with the Free Folk, most commonly with the Haragni, one of the oldest of the wildling tribes. The act of scalping has been practised for centuries and is believed to have been developed sometime after the diversification of the First Men cultures.
The Haragni wear their scalped victim's heads as trophies on their shoulders, usually to inflict fear into their enemies when on the battlefield. It is also believed that the Haragni use their scalps as some sort of ritualistic or symbolic practice. The act of scalping is highly taboo south of the Wall and is rarely ever practised. Those who do practise scalping are usually arrested and convicted. The penalty for practising scalping is death.
Using the corpse of Mortin as a decoy, Lucius Dragen ambushes Manwell. He chases him into the woods and they engage in a bloody fight beside the shores of the White Knife. Lucius is about to kill Manwell, but stops when he notices a group of Haragni at the other side of the river. He pushes Manwell downstream into the hands of the wildlings. Ferwyn scalps and kills Manwell, but spares Lucius. Manwell's scalped body floats away downriver, with the Haragni keeping his scalp as a trophy.
- Scalping on Wikipedia