The now-settled lawsuits brought by thousands of former players hinged on the notion that the NFL ignored decades of research on the degenerative long-term effects of brain trauma, and didn't take enough steps to protect its employees. Here's a helpful (ahem, Pete Prisco), but necessarily incomplete timeline of concussion research and the NFL's response. Some of this relies on the excellent timeline put together by Ta-Nehisi Coates and Malcolm Burnley.
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