A research team from five different countries conducted a review of 7,673 articles on the incidence of concussion among top athletes aged 17 or older. In their meta-analysis they found the highest number of concussions at rugby matches and the lowest number during men's football training. Generally, concussions and head injuries were rare during training compared to competitions. Female players had an increased risk of concussion in football and ice hockey compared to men.
Sports Med. 2018 Jan 18. doi: 10.1007 / s40279-017-0854-4.