Let's take your hypothesis and discuss.
The medical community did not know about the issues with concussions when these injuries were happening.
Ok, a few questions now:
1. Should they have known? Should the NFL have commissioned studies earlier to protect the players? Does the NFL, as employer, have a duty to protect its workers or a special duty to learn of long term health issues they may face b/c of their employment?
2. Who was in the best position to know? A team with billions of dollars, or a football player who may not have even graduated from college?
3. Even if no duty existed, and the NFL had no reason to perform any proactive investigation, who should pay now? Keep in mind that a player who cannot afford the treatment for his serious injuries is forced to treat at a public hospital, meaning you and I, as taxpayers, pay for his treatment.
So with that in mind, even if the NFL has completely clean hands (it doesn't but just assume for a second), is it better for us to have to take care of him with our tax revenues, or for the league that has made billions on the backs of these players to have to take care of it?