Mechanism of Injury

More often than not, concussion occurs due to direct contact with another player, as opposed to contact with playing equipment, but it should also be remembered that striking the ground fixtures such as goalposts can also provide enough force to result in a concussion.
Impact studies show that forces from 20 to 180 G can be sustained by players without either concussion symptoms or changes in objective testing.
Similarly, players have been reported to be either a concussed or knocked out after sustaining impacts less than 40 G.
However it is yet to be established if there is a specific G force of impact which can reliably predict concussion.

Gessel LM, Fields SK, Collins CL, et al. Concussions among United States high school and collegiate athletes. J Athl Train. 2007;42(4):495–503