Most 40-yard dash times are hand-held and open to a significant amount of human error. Many track times, however, are electronic and can give a more accurate gauge of speed. The following chart can be used to help verify reported 40 times of football players who also run track. It gives a rough estimate of the equivalent 40 time that matches an electronic 100 time. In short, if a guy is reporting he runs a 4.3 in football, he needs to have a blazing 10.3 or better time documented in a 100m track time.
The story linked below the chart goes on to explain how overblown many 40 times are, and that there just aren't that many people out there running 4.4s or better. That is exceptionally rare speed.
10.2 = 4.34
10.3 = 4.38
10.4 = 4.43
10.5 = 4.49
10.6 = 4.54
10.7 = 4.58
10.8 = 4.63
10.9 = 4.75
11.0 = 4.85
How Fast Is Fast? Breaking Down 40 Myths
The story linked below the chart goes on to explain how overblown many 40 times are, and that there just aren't that many people out there running 4.4s or better. That is exceptionally rare speed.
10.2 = 4.34
10.3 = 4.38
10.4 = 4.43
10.5 = 4.49
10.6 = 4.54
10.7 = 4.58
10.8 = 4.63
10.9 = 4.75
11.0 = 4.85
How Fast Is Fast? Breaking Down 40 Myths