There is a big concern about concussions in sports especially football.
The first thing to do is know what a concussion really is. The root word comes from the Latin word "concussus" meaning the action of striking together. This means that any time you are hit in the head you have had a "concussion". Sometimes this blow results in Traumatic Brain Injury (TBI). This is what is really being discussed not the simple blow.
There are some "simple" rating systems that grade 1,2 or 3 based on presence of loss of consciousness and amnesia. There is a more complicated system that grades a series of "lesser" symptoms on a scale of 0 to 6. It is called the Sport Concussion Assessment Tool. This can be used by anyone to make a decent assessment.
It is estimated that on average the annual number of 595,095 TBIs are due to falls. Another 292,202 are motor vehicle–trafﬁc TBIs. There are about 279,882 due to being struck by/against events, and 169,625 are assault-related TBIs. Motor vehicle–trafﬁc resulted in the greatest number of TBI-related deaths. Falls result in the greatest number of emergency department visits and hospitalizations.
7% of all injuries to BMX riders are TBI. Studies have shown a decrease of TBI by waiting until a child is 7 or 8 to start riding bikes. Bicycle helmets have reduced TBI in children 17 and under but no change over that age.
Some experts want to start using the term Mild Traumatic Brain Injury (mTBI) to describe the injury. This is more specific that just saying "hit on the head".
Some data from an article here the letters refer to the specific sources for that data.
SportInjury Rate, per 1000 Athlete Exposures
Boys' and girls' volleyball
One thing to note is the much higher incidence of TBI in females vs males in soccer and basketball.
Perhaps this will give some basis for people to react about this currently controversial and "popular" subject.