The basic guidelines are:
As a minimum, lightning safety experts strongly recommend that
by the time the monitor observes 30 seconds between seeing the
lightning flash and hearing its associated thunder, all individuals
should have left the athletics site and reached a safer structure or
location.
To resume athletics activities, lightning safety experts recommend
waiting 30 minutes after both the last sound of thunder and last flash
of lightning. If lightning is seen without hearing thunder, lightning
may be out of range and therefore less likely to be a significant
threat. At night, be aware that lightning can be visible at a much
greater distance than during the day as clouds are being lit from
the inside by lightning. This greater distance may mean that the
lightning is no longer a significant threat. At night, use both the
sound of thunder and seeing the lightning channel itself to decide
on resetting the 30-minute "return-to-play" clock before resuming
outdoor athletics activities.
Almost every college has a system, such as the SkyScan Lightning/Storm Detector, in place to assist game managers in their decisions when it's safe to resume play.
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In high school, as soon as thunder is heard or a cloud-to-ground lightning bolt is seen, play is suspended for 30 minutes. In college, they usually measure the time between seeing the lightning bolt and hearing the thunderclap, and if it is less than 30 seconds, play is suspended for 30 minutes.
The NFL purportedly has similar guidelines, but they seem to enforce them only in the gravest situations.