Defensive players chase and at the same time have to avoid being blocked. Some chase more and avoid blocks less. DL the other way around. Some are very good at instinctively positioning themselves so they do both very well.
Offensive players, it's a bit more specialized. Guys like Rice could "see" opponent's balance and change directions at precise imbalance moments so they are very hard to catch or cover. There are some relatively slow players that are very hard to catch or cover. Acceleration, which encompasses, starting, stopping, and changing direction is huge. But this can be offset by the ability to read an opponents body language; To feel an off balanced opponent, whether engaged, or in an open field situation.
Track... BS for football. Sure it helps to be fast. But chasing and avoiding being caught are fundamental. The film tells so much more.
Coaches take note, Clowney was absolutely gassed in a number of games this season. Figure out why.