A study jointly conducted by Cleveland Clinic and the University of Rochester suggests football players who don't suffer concussions may still experience brain disorders due to sub-concussive blows to the head.
The study involved a brain injury assessment for 67 college football players; the assessment included blood tests, brain scans, and a review of game footage to account for blows to the head these players had received during play. Blood tests revealed that four of these players demonstrated the presence of the protein S100B in the bloodstream and an autoimmune response to S100B associated with damage to brain tissue. Long term effects associated with this damage include epilepsy and dementia.
The blood test for S100B may offer an inexpensive and objective metric for directly correlating in-game sub-concussive head impact with the amount of medical attention required for the players who suffer these impacts.
Marchi N, Bazarian J, et al. Consequences of Repeated Blood-Brain Barrier Disruption in Football Players. PLoS ONE. (March 2013).