Then came a great fall of "hailstones"--the Hebrew word is used elsewhere only of true hail--which killed still more of the Amorite horde. This implies a unique atmospheric upheaval, probably occasioned by a swift deceleration of the earth's rotation.

Source:

KJV Defenders Study Bible, by Dr. Henry Morris, Ph.D.
Publisher: Thomas Nelson
Language: English
DEF 10 ISBN 0-529-10444-x
DEF 10-1 ISBN 0-529-10445-8