It’s hard to stand out in the NFL draft process if you are not a good athlete. Compared to most people on the street, most players who make it as far as the draft are phenomenal athletes, but it is often the truly monstrous physical specimens who rise to the top and, if a prospect tests at a below average level at the Combine or at his pro day, the odds of them succeeding in the pros can be dramatically reduced.
Still, there are ways to compensate for a lack of athleticism, even at a position such as safety where it would seem to be a prerequisite.