Be riveted to the spot/ground
Definition 1 of 1
Pro Tip 1/3Intensity Required
Use the phrase when describing a moment of intense emotion, not just mild surprise or interest. 
Hearing the verdict, she was riveted to the spot in disbelief.
Pro Tip 2/3Literary Use
Often found in literature to describe a character's reaction to a dramatic event. 
In the novel, he was riveted to the ground when he spotted the dragon.
Pro Tip 3/3Not Literal
It's usually metaphorical; the person is not physically unable to move, just emotionally halted. 
At her surprise party, Emma was riveted to the spot with joy.