"To the Editor: Soccer is the most popular sport in the world, with more than 250 million active players.1 It is the only sport in which the unprotected head is a primary point of contact when heading the ball. In other contact sports, the deleterious long-term effects of repetitive traumatic brain injury (TBI), such as impaired white matter integrity,2 are well recognized.3 However, whether frequent subconcussive blows to the head lead to TBI remains controversial,4- 5 although evidence suggests impaired neuropsychological function in soccer players.5 We evaluated concussion-naive soccer players using high-resolution diffusion tensor imaging (DTI), which is highly sensitive for detecting alterations in white matter architecture."
Heads can also hit each other or goalposts, for example when a keeper dives for the ball.