I have seen claims that NFL football players can run 40 yards in well under 5 seconds. Some claims are as low as 4.1 to 4.2 seconds. Claims of 4.4 to 4.7 seconds have been made for (I think) 20-30 years. These speeds seem to be due to exaggeration and/or faulty timers. I did an analysis based on split times for world class sprinters. An estimate based on split times for a 1991 world record 100 meter race was 4.38 seconds for 40 yards. An estimate based on a more recent race was 4.31 seconds. An estimate based on a disallowed world record race was 4.26 seconds. Since the final time for that race was disallowed as a world record, I do not consider the estimated time for 40 yards to be valid (There was perhaps aide from the wind or a sloped track). Note that World Class sprinters do more intensive training for sprinting speed than do NFL players. World class sprinters also run on a surface better suited to running speed and wear shoes better suited to sprinting. Based on the above, I doubt if many NFL players can run 40 yards in much under 5 seconds. Perhaps 4.8 seconds might be possible for the fastest players. Carl Lewis, though no longer holding the world record, has the fastest recorded time of .83 seconds for 10 meters. This indicates that he could run 40 yards in about 3.03 seconds with a running start. I wonder if NFL players are timed with a running start. I wonder if the claimed times are due to Public Relations hype or faulty timers. Does anyone here have any knowledge relating to the above?