Just throwing this out. The issue with the long term loss of brain function, according to studies, is not just from trauma like concussion, but is from lower impact repetitive blows to the head. Thus the issue, whether with soccer or with football is not how many violent injuries occur but rather the number of times a person experiences low impacts that impact the brain. So if you head a soccer ball over and over in practice it is the cumulative effect over years that is the problem. Same with football. It does not even have to directly involve the head. Again the issue is not so much a direct blow to the skull, thought that is certainly not good, but rather the number of times the brain is jarred inside the fluid of the brain.