It's the brain shutting down from lesser impact than before due to accumulating damage, there's not some magic mechanism that wears out and causes easy KOs, it's an issue of damage to the brain. In severe cases of PCS a person can experience a concussion just from shaking their head. E.g army vets and car accident survivors.
It's an ugly aspect of any combat sport, and football.
You said no reference to this but not doing so wouldn;t be answering the question properly.
Last edited by Hiro; 11-23-2010 at 12:38 PM.