Yup. One of those "soft" injuries that aren't always easy to diagnose, though that could be said about a lot of injuries. Players suffering the effects of a concussion are notoriously unreliable about reporting symptoms.Concussions aren't always easy to diagnose, and the player needs to reporting symptoms honestly to do so in mild cases.
We know not all players are willing to do so...
I mean, it's a brain injury! Of course they're not thinking straight.