It is, as the concussion specialist Robert Cantu argues, with repetitive subconcussive trauma.

NEWYORKER: Offensive Play

Dr. Robert Cantu takes a more measured view.

NPR: Mixed Martial Arts: Sport or Spectacle?

First, note that Sports Legacy Institute, Dr. Robert Cantu, and Mr. Chris Nowinski should be highly commended for their tireless efforts to further the research on correlations between competitive athletics, head trauma, and long-term health repercussions.

FORBES: CTE Research, NFL's Financial Headache, and Tobacco Industry