Soccer is not a violent game. But players can hit the ball with their head to purposely change the direction of the ball. In the sport this move is known as a header. Unfortunately, they may sometimes crash into other players, the ground or goal posts. During the World Cup semifinal soccer match in Sao Paulo, Brazil, July 2014,Netherlands,Dirk Kuyt went for a header with Argentina's Javier Mascherano and Ezequiel Garay, making his competitors injured in head. Catherine McGill is a neuropsychologist  at the Children's National Health System in Houston. She examines many children who have suffered concussions  ,which are the most common brain injury. She says concussions from soccer and other youth sports are increasing. "Firstly,parents, coaches, and medical providers alike are getting better at recognizing and responding to the injury, and it,s a huge proof to media paying more attention to this and leagues  paying more attention to the safety of their players. Also, kids are getting bigger, faster, stronger across the sports, and so more injuries may be occurring simply because of that." Catherine McGill spoke at a recent conference on ways to make soccer safer for young players which was held recently in New York. She says researchers are examining the effects of soccer-related head injuries. They want to know whether repeated hits to the head can cause CTE, which is a brain disorder that worsens as a person ages. She says parents often ask what age children should start "heading" or whether there should be "heading" at all. She thinks it,s a very individual decision. The age for one child may be quite different from another. According to the passage, Dirk Kuyt is probably  _  .
a league leader a soccer player a doctor a coach