10 second barrier

The 10-second barrier is a term used in track and field athletics, which refers to the physical and psychological barrier of completing the men's 100 metres sprint in under ten seconds. The achievement was traditionally regarded as the hallmark of a world-class sprinter. Its significance has become less important since the late 1990s, as an increasing number of runners have surpassed the ten seconds mark.

For sprints, the International Association of Athletics Federations (IAAF) rules for world records and other recognised performances require: a wind assistance of not more than two metres per second (7.2 kilometres per hour (4.5 mph)) in the direction of travel; fully automatic timing (FAT) to one hundredth of a second; and no use of performance-enhancing substances.Wind gauge malfunctions or infractions may invalidate a sprinter's time.

Prior to 1977, FAT was not required for IAAF official timings. Times were recorded manually to one tenth of a second; three official timers with stopwatches noted when the starting gun flashed and when the runner crossed the finish line, and their median recorded time was the official mark. Some races also had an unofficial FAT, or semi-automatic time, often in conjunction with photo finish equipment. The first person timed at under ten seconds was Bob Hayes, who ran 9.9 s in April 1963 at the Mt. SAC Relays with an illegal following wind of 11 mph (4.9 m/s). Hayes clocked another illegal 9.9 s (wind 5.3 m/s (12 mph)) in the semi-final of the 1964 Olympic 100 m, with the first sub-10 FAT of 9.91 s. In the final, Hayes' official tenths time of 10.0 s was calculated by rounding down the FAT of 10.06 s; the backup hand-timers recorded 9.8, 9.9, and 9.9, which would have given 9.9 s as the official time if the FAT had malfunctioned. At the 1968 USA Outdoor Track and Field Championships at Charles C. Hughes Stadium in Sacramento, California, United States, three men ran legal hand-timed 9.9 seconds: Jim Hines first and Ronnie Ray Smith second in the first semi-final, and Charlie Greene first in the second semi-final. This was dubbed the "Night of Speed", and all three were recognised as world records by the IAAF. The IAAF lists their FATs as: Hines 10.03, Smith 10.14 and Greene 10.10; although Time magazine reported at the time that "an automatic Bulova Accutron Phototimer confirmed that all three had indeed broken [10.0s]". Hines also had a wind-assisted 9.8 s in the heats. Hines went on to win the 1968 Olympic 100m in 9.9 s, rounded down from his FAT of 9.95, making it the first non-wind-assisted electronic sub-10-second performance. By 1976, six other men had equalled the 9.9 s hand-timed record, though none of their performances had an FAT mark.

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