This is a thorough, but very Frontline, overview of CTE back in 2013, right when the NFL lawsuit happened. It’s very clear it was mostly assembled beforehand, and then a few additional aspects of the story broke and they were incorporated into it before it aired.
So overall, this is a pretty good summary of the state of CTE research in 2012 ish. It’s obvious Frontline is on the side of the scientists and journalists looking into CTE, as the episode is in part based on a book about this. If you’re looking for an objective summary of the science at the time, you’ll only get a few concessions to the problems with the Boston University sample (nowhere near a random one) and the issues of causation (we really don’t know what is actually the causal factor).
But, given journalism’s role in speaking truth to power, it’s hard to quibble here. Not only because the episode is on the side of the players whose lives have been ruined but because of the NFL’s various positions over the years, most of which have been to deny it in some way or other. It’s not unlike the debate over vaccines and other public health measures during the 2020 pandemic: it’s one thing to want scientific certainty when you have time on your side, and you’re not in a crisis. But sometimes an educated guess has to suffice for the time being. In this case, if I was a parent in particular, an educated guess that CTE in football players is partially caused by football is a better bet than “I have to wait for the science.” And every time you hear a scientist say “we have to wait for the science” you kind of wonder who they are protecting. It’s not the players.
It could be a little better organized, as it feels like the last few sections were tacked on at the end but otherwise it’s worth watching if you’re interested even though it’s now out of date.