Charles Ellicott Commentary Exodus 9:23

"And Moses stretched forth his rod toward heaven: and Jehovah sent thunder and hail, and fire ran down unto the earth; and Jehovah rained hail upon the land of Egypt." — Exodus 9:23 (ASV)

The fire ran along upon the ground. —Heb., fire walked earthwards. Kalisch and Knobel interpret this as mere ordinary lightning, but Aben-Ezra, Canon Cook, and others think the phenomenon was as our Version aptly describes it.

There is no doubt that electric fluid occasionally takes a somewhat permanent form, lasting for several seconds, or even minutes, either stationary or moving slowly. Appearances of this kind have been called “fire-balls” and indicate an excessive electrical disturbance, involving great peril to life and property.

Even if the expression “fire walked earthwards” does not itself imply such a phenomenon, the specific phrase in Exodus 9:24 seems to suggest it.