The scrum cap is a form of headgear used by rugby players to protect the ears in the scrum, which can otherwise suffer injuries leading to the condition commonly known as cauliflower ears. Although originally designed for forwards they are now worn by players of all positions, even those who do not play in the scrum.
A simpler alternative to a cap, or a head-cap and used by many players, is a thin strip of foam or cloth and electrical tape wrapped around the ears like a head band.