It's probably pointless to argue at this point, but it's apples and oranges. Yes, Big Ben knows he is putting his foot at risk when he does what he does.
But until recently, the extent of damage done permanently by concussions was poorly understood. The lawsuits don't say that the players didn't know they were hurting themselves; it says that the NFL knew more than they let on about the permanent damage of cumulative concussions. The players didn't know that ALS, etc could be caused by concussions, the belief was that once you recovered from it you were fine -- the allegation is that the NFL did know more, and didn't do enough to educate and protect the players from that cumulative damage.
The "players didn't know they were at risk from playing football" line is purely a strawman, and adds nothing to the discussion. That's not what they are claiming.