Catching a Young or Unhandled Horse - Dr John Kohnke BVSc. RDA

Catching a young, unbroken horse can be both dangerous and time
consuming. You can try to corner such a horse with another horse, but
the young horse usually gets in behind the horse being held and can’t be
reached.
As a vet, the most successful way I find is to get the horse into a corner and have one person helping by standing across the escape line. Keep all dogs, children, on-lookers and other horses away - this is most important. Only the person trying to catch the horse moves or speaks - the other(s) must stay mute. Talk softly to the horse and look it in the eye at all times - never become distracted. Slowly move in towards the horse on the near side with a headstall and rope in the left hand. Use your right hand, with the back of the hand towards the horse, to gain the horse’s attention by gently wave it up and down continuously in a set pattern, as if to stroke the horse on the neck.
This movement, combined with looking the horse in the eye and gently talking to it in a soft monotone, seems to mesmerize the horse. Keep slowly moving forward until the right hand gently makes contact with the neck, talking softly to the horse all the time.
Then gently stroke the neck for 10-15 seconds to help settle the horse, softly talking to the horse and looking it in the eye. Don’t take your eyes off the horse - look it in the eye at all times. Do not make any quick movements and while stroking the neck with the back of the right hand, bring up the headstall in the left hand and gently put the lead around the neck, then slowly fit the headstall to the head, talking to the horse the whole time and looking it in the eye.
I find it is a waste of time trying to offer feed. The gentle, hand stroking approach is the best.
Once caught, leave the headstall on for a few days on a foal or young horse with a short lead rope about 40cm hanging down. Repeat the same catching technique
each day for a few days and most horses, unless they are completely feral (or
need a new owner) are broken to be caught.

Article courtesy of Dr John Kohnke BVSc. RDA - Talking Horses newsletter