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).
Is it possible that it's the most widely played sport (and some of the least protective equipment) so they'll see the most people but it might not be the highest per capita?
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.
And soccer has the most injuries of any sport, according to an ER doc (who treated me for a football injury).