Exodus 9:23 - Ellicott's Commentary On The Whole Bible

The fire ran along upon the ground. — Heb., fire walked earthwards. Kalisch and Knobel understand by this mere ordinary lightning, but Aben-Ezra, Canon Cook, and others think that the phenomenon was such as our Version well expresses. There is no doubt that the electric fluid occasionally takes a form which has something of permanency, continuing several seconds, or even minutes, either stationary or with a slow motion. Appearances of this kind have been called “fire-balls,” and indicate an excessive electrical disturbance, involving great peril to life and property. If the expression “fire walked earthwards” does not imply anything of this kind, yet the peculiar phrase of Exodus 9:24 would seem to do so.