read it here
and I know it is from BR, but it is very well written.Ridley immediately lost consciousness due to the hit, made obvious by his body going limp, the fumble that resulted and his posture on the ground immediately following the tackle. The large amount of rotational force applied to Ridley was likely to blame.
The brain stem is particularly sensitive to rotational forces, and within the brainstem is the reticular activating system (RAS)—the part of the brain responsible for maintaining consciousness. By causing the cellular changes mentioned above, those rotational forces briefly stunned Ridley's RAS and caused him to lose consciousness.
Similar changes in the brain stem also caused Ridley's "fencing response."
When Ridley hit the ground, he held his left arm—the side of the head that was hit—straight out in front of him and right arm—the side of the head not hit—bent in toward his side for a few seconds.
However, he didn't know he was doing so. Believe it or not, his motions were actually reflexive.
Hope he has a full recovery!