The 10-yard splits can indicate a receiver’s initial burst off the line (often the most important skill for a receiver’s translation to the pro game) or a running back's initial speed at the hand-off point.
The most recognizable activity at the NFL Combine each year, the marquee event is meant to show players' top-end speed. Starting from a stationary position, players' 40-yard dash times give an indication of their speed from a standstill.
While many are critical of the 40’s value in evaluation, it does matter. It’s easily replicable and comparable across all athletes, thereby giving a uniform measure to evaluate speed.
For offensive and defensive linemen, merely looking the part of an NFL athlete can have more value than the actual time, and running under a 5.3 as a lineman serves as a strong benchmark in evaluations.