DK Note: I wrote this article that breaks down the NFL Combine and all its tests back in 2014 -- so the player examples are all pretty outdated, obviously -- but the concepts discussed still apply well today.
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Prior to 1985, three NFL scouting organizations existed for the purpose of evaluating college prospects - The National, Quadra and BLESTO - and they all ran their own scouting events. That year, the three organizations, in the interest of logistics, combined forces (get it?) and formed what's now known as the NFL Combine.