I wrote about this subject a year or two ago. The 40 yard dash is an artificial and random event and does not give an accurate reading on speed. In fact most all of the tests they use at the combine are not true indicators of athletic feats. That would include the vertical leap. The best way to measure athleticism is to use standard Olympic events. Want to test leaping ability then have them perform the high jump and or long jump. Want to test their sprinting ability then have them run the 100 meters or at the very least 100 yards which used to be a measuring stick for wide receivers back in the 60's. Want to test their strength then have them do Olympic type weightlifting and or have them throw a shot put. For endurance have them run a marathon or the steeple chase. How about the hurdles for agility? Football players are generally not running 40 yards or even 20 or 10 yards. Yes they could cover that amount of space on any given play but unlike track and field there is more than just "one take." There are many plays so a player is running and running and running far greater than 40 yards especially when one team controls the ball. For running speed only the 100 yard dash will give you a better idea because during the course of a game a player is constantly running so any 40 yard dash time will be skewered by the fact that their endurance isn't being factored in when they run these Combine 40 yard dashes. One example of many. If a CB has just covered the equivalent of 100 yards over the course of three consecutive plays doesn't it stand to reason that the 40 yard dash time he ran in a controlled artificial environment while he was as fresh as a daisy doesn't translate to a player running many more yards with just minimal breaks in between plays. The 40 yard dash and the vertical leap verge on gimmickry and young black youths concentrate on these one trick pony feats at a very early age. Now a player that runs a fast 40 could run a fast 100 yard dash as well but there is no guarantee . Ultimately there is way too much reliance on the 40 yard dash and at the end of the day as it relates to football doesn't provide an accurate enough measurement of speed as far as I am concerned. Heck baseball players even have a longer sprint than football players as the 60 yard dash is the staple measuring stick for speed. And baseball fields are a lot smaller than football fields.