rooted to the spot - Phrases/Idioms
The American Heritage® Dictionary of Idioms by Christine Ammer. Copyright © 2003, 1997 by The Christine Ammer 1992 Trust. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.
Not moving, especially owing to some strong emotion. For example, When the truck bore down on the dog, he was terrified and stood rooted to the spot. This idiom likens the roots of a plant to a strong feeling that keeps one from moving.