GAINESVILLE, Fla.  Last April, during spring football practice at the University of Florida, a collective gasp came from a track meet across the street. Jeffrey Demps had just run the fifth-fastest 100 meters by an American high school sprinter, 10.17 seconds. Even better, he was a Gators football recruit.

“The rest of the day, I’m not really sure what happened at practice,” said Coach Urban Meyer, who heard the time over the public-address system. “I was so excited we had a guy joining the program that could run sub-10.2. I’ve never witnessed that.”

In late June, at the Olympic track and field trials, Demps ran even faster, setting a national high school record of 10.01 and matching the world junior record for the 100  a time equal to the seventh-place finish at the Beijing Games. Now a freshman tailback at fifth-ranked Florida, he appears to be the swiftest running back ever to play college or professional football, according to track historians and an examination of performance lists compiled by USA Track and Field.

At 18, Demps is already much faster than famous predecessors like Herschel Walker (10.23), O. J. Simpson (10.3) and Bo Jackson (10.44), slightly faster even than Bob Hayes (10.05), the 1964 Olympic champion at 100 meters who played running back at Florida A.&M. before becoming an All-Pro receiver with the Dallas Cowboys.