Environmental toxins may play a role, watching too much television may play a role, and excessive stimulation may play a role.

NPR: Excerpt: 'Delivered from Distraction'

Serious foul play is classed as when a player "uses excessive force or brutality against an opponent when challenging for the ball when it is play".

BBC: Terry wins appeal to face Man Utd

The Emory researchers think this same sleep-inducing substance in spinal fluid may play a role in other conditions that involve excessive drowsiness.

WSJ: Unraveling the Riddle of Too Much Sleep

Wenger initially reacted by saying that Taylor "should never play football again" but later conceded that his comments were "excessive".

BBC: Arsene Wenger admits Jack Wilshere deserved red card