That depends. They are herd animals so the tendency would be to bolt and leave the area. Some horses are different tough. Ivan, my walker, will freeze up completely whenever anything scares him. He has never bolted and ran. Other horses I have owned will try to flee instantly.
A horse's first instinct if it is afraid is to run.
When a horse is frightened or afraid their first instinct is to Flee, run or get away. known as spooking.
to bite
It will bolt.!
Bolt.
flight or fight and if it is afraid it is going to have a flight instinct
A horse's first instinct when frightened or startled is to run away. The second instinct is to fight in order to protect itself.
A horses first instinct when fearful is almost always to flee first and ask questions later. In some cases though the horse is attack, but that is not common.
run away
Horse will Flee
For Howrse it's answer is Flee.
horses first instinct is to run, to get away from whatever is scaring them and if all else fails, defend itself. -HorseOwner