My understanding is that the concussions in soccer come from direct head-to-head collisions (which are not cushioned by helmets) and from heading the ball (which is moving significantly faster than a human being). The fact that you find the similar concussion rates between these two sports surprising is good reason for you to doubt your ability to identify dangerous sports based on your intuition for how violent they are.
Head to head collisions are relatively rare. You could play an entire career without getting one. Heading the ball isn't that bad, actually, and certainly doesn't happen often. Players can go through a season without ever doing it.
Either you don't watch much Football, or you don't watch much American Football. One only needs to watch a few games of each to see how violent they are. American Football has dozens of people smashing into each other (often head-first) every minute of the game.
Much more than other sports? No, I don't think so. Modern concussion tracking studies take baseline cognitive measurements and then periodically re-measure throughout the year, regardless of whether the player reports an injury.
Somebody ran a survey where they looked for replies that indicated "probable" concussions that were unreported, and they found
> The sports with the most unreported concussions were women’s soccer (24%), men’s football (21%), field hockey (13%), and cheerleading (10%).
I don't believe those numbers are normalized for the number of concussions, and in any case would indicate that women soccer players were slightly less likely than football players to report a concussion conditional on having one.
As for "unrecognized" concussions (i.e. the athlete gave a reply on the survey that sounded like maybe they had a concussion) they say
> The sports with highest potentially unrecognized concussions were football (55%), cheerleading (50%), and cross-country (28%).
which to me means you can't trust this survey at all. Whatever they're interpretting as an "unrecognized" concussion, it happens as often in cheerleading and over half as often in cross-country.
On the other hand, if you want a human interest piece, you can go read skierscott's link to the NYTimes blog post about how all those football players are toughing out brain damage....
Every time some one does a study they find they're under reported in every sport. They might be more underreported in football but its also under more scrutiny so its hard to say who knows how the reporting rates compare.
