Earlier quoted context omitted.
There are martial arts where even in competition, concussion is relatively rare. E.g. grappling sports like Brazilian Jiu-Jitsu don't usually involve impacts of that intensity, to the head or otherwise.
Football has more concussions than boxing, because it has more full speed competition than boxing. Almost nobody does in-the-ring boxing, they just learn. And soccer has the most injuries of any sport, according to an ER doc (who treated me for a football injury).
That said, I know a kid who somehow lacerated his kidney and had to spend time in the ICU. At least two others with concussions.