Concussions are a big problem in rugby too, and they have only relatively recently realised the extent of the issue. The NFL may have swept the issue under the carpet for years, but everyone was burying their head in the sand until very recently in rugby - there have been multiple cases of players clearly getting knocked out and playing on after a short head injury assessment this decade.
There are many accounts of players saying they don't remember huge periods of matches. Shonatayne Hape gave a great interview which is absolutely terrifying, where he describes the effects and how it became progressively easier for him to lose consciousness to the point where he didn't even have to been hit in the head by the time he retired:
Former UFC champion George Saint-Pierre has described in interviews how he basically loses consciousness for hours at a time, and doesn't know what happened. Like he'll come to and an entire day has passed. He suspects alien abductions (!), but there's no doubt this is brain trauma from all the hits to the head in MMA.
There are many accounts of players saying they don't remember huge periods of matches. Shonatayne Hape gave a great interview which is absolutely terrifying, where he describes the effects and how it became progressively easier for him to lose consciousness to the point where he didn't even have to been hit in the head by the time he retired:
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