Horses are most likely to kick on their 1st instinct. This is why you never need to walk/stand behind a horse or try to scare one.
To Fight Or Kick.
its first instinct is usually to flee from that person but depends how scared it is if its not that scared it will just bite
A horse's first instinct if it is afraid is to run.
A horse's first instinct when frightened or startled is to run away. The second instinct is to fight in order to protect itself.
Horses are fight or flight animals. When they're scared they might spook. Then they'll either try to defend themselves and kick and bite, or they'll run away.
horses first instinct is to run, to get away from whatever is scaring them and if all else fails, defend itself. -HorseOwner
It scared the horses.
A horse's first instinct, if scared, is to flee. That is why horses have such long legs; they're built for speed. That is also why horses bolt. Horses in the wild, live out in the open to see danger coming so they can get a head-start. Horses have eyes on the side of their head; to watch for danger. Horses generally sleep standing up, so they can be prepared to run. A horse will only try to fight if cornered. : )
It will put both ears flat against his/her head. If you are riding the horse, hold on tight! The horse could buck, rear, or take off if it is scared enough. Get the horse in a safe shelter.
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.
the answer is kick so don't stand behind a horse and make it scared
It is an instinct when they are scared or upset.