My seasoned broodmare showed signs of premature delivery and upon advice of attending vet, I took the mare to a great vet hospital for the delivery. It was very successful but required a lot of “hands on” with baby, who was born on July 20th. We were finally able to bring him home today (very exciting!) and I kept the barn quiet and handling to a minimum. He’s been such a sweetie so I was shocked when for seemingly no reason he charged me, ears flat back, gums barred. When I just stared at him and barked a sharp “No!”, he turned around and tried kicking me! Mom has a fabulous temperament as does dad (I don’t breed ill-tempered animals - for a good reason!). I’ve been doing this almost 40 years and have never had this happen - I suspect all the handling in a hospital setting has made him cranky, the 80 minute trailer ride home left him exhausted, but I’m clueless as to how to deal with this crazy behavior and I most certainly want to nip it in the bud while he’s only 200 pounds. I believe in positive-reinforcement with my training, or at least allowing a horse the avenues for making “easier choices” as opposed to punitive training. Help?
Personally for me aggression is the one thing with foals where I DO believe in punative response. It must be swift and firm. It is dangerous and needs to be nipped now. Aggression issues are not the place for “positive reinforcement” like haltering and training. The sharp NO is a good place to start but if that does not work then a wiffle bat (harmless but noisy) or short/quick smack with a crop accompanied by the NO is in order. Think like a horse. If he kicked another horse is herd what would they do? They would kick back to put him in his place. And I guarantee you that a horse kicking him will hurt a helluva lot worse than a wiffle bat. Has he had any turnout with other horses or been solo due to the illness? All foals go through a phase where they will try and climb up the social ladder and get pushy…but ones that have not been with other horses to “discipline them in the herd” tend to try it on you more.It is a social skill.
You have the experience and IMO, the right train of thought to handle this. 
Has he been on and is he still on ulcers meds? Pick your battles. I would take a step back and handle minimally, which it sounds like you are doing. Do not look for a fight, but of course, do not tolerate bad behavior. I’ve found ignoring the foal and doting on the mare is almost unbearable to a foal. They can’t help but come over to investigate.
Grab him around the chest and bum and hold him till his ears are forward and he is quiet. Funny, my three year old still thinks if my hand is on his chest he cannont move forward and all I did was hold him a couple of times when he was little.
I agree with the whiffle bat. If he comes at you in this way again a good whack to the chest will get the message across, it won’t hurt him but the noise will probably scare the heck out of him. He is probably feeling pretty good now and being almost 2 weeks old he is ( hopefully) not stalled but has plenty of room to self exercise 24/7?
We have had this experience with foals who are scared or who are in pain (one newborn was hideously ugly to us and we found had an umbilical abscess - we feared giving shots 2x daily would make it worse but he actually was completely friendly by day 3 because he felt SO much better!). Another we had was just simply scared of us and being very aggressive as a result. I still agree with others that it needs to be corrected quickly and sharply though, as he’s probably either scared in his new situation or sick of being messed with, like you said.
Either way, he’s not allowed to be ugly. I use a sharp and strong slap on the butt immediately timed right after they turn and kick and after a few times they scamper away giving the “baby mouth” (“clacking”) and then you know they are submitting. We’ve never had it come up again after the inital “come to jesus meeting”… We had a colt this year come home with mom after she colicked right after birth and went to NC State when he was 8 hours old… they thought it was cute to let him kick, and he was rambunctuous after 5 days in a stall as a newborn - so we had a few attempted double barrells and a few retaliations on my part and all was solved in about 15 minutes. 
Fear = respect at the most basic level so it’s ok for him to be a little afraid of you at first, he’ll come around! Good luck!
A foal is a horse in miniature.
They will try things because they’re a blank slate. Each behavior has a causative consequence. Give him the consequences to his actions. These things are training opportunities and they can only learn something when moments like these arise.
While it is okay to show an angry face during punative action when they do something wrong like bite or kick or show some momentary naughty behavior, once you achieve the desired response to your punative action (ie him backing down), make sure you drop it - drop your face and drop your response and let it go like it never happened.
If you watch your mares they do the same thing. They charge and discipline the culprit, with a bite and swift kick, and then it’s over and that’s that. They don’t harp on it on and on and on and they don’t hold grudges.
Just make sure you react fast - if you delay your timing you’ve lost out on a training opportunity. Sometimes always carrying something doesn’t work because they learn not to try things when you have a “weapon”. Then, the second you don’t have a weapon, they’ll try it again. So, make use of your own hands and body. I nearly knocked a colt off his feet once because he tried to rear and push me with his knees. I put on my “angry face” got right into his eyeballs, stuck my jaw out (to imitate a mare snaking at her intended target) and made full body contact like a good football linebacker. Imagine his surprise as he scuttled back behind mom (who stayed eating her hay) and peeked at me from under her belly. He wasn’t afraid of me, but he had a whole lotta respect for me because I was “bigger than he thought” and he knew I wasn’t playing around. Even foals quickly learn whether you are a person who means what you say and says what you mean.
Everything you mentioned is exactly what I was going to say. I wonder if he might have an ulcer brewing…but in the meantime, he needs to understand the social ladder. Hugging and holding and positive reinforcement is not going to do it for this type of situation It’s not what would happen in a heard situation…and he needs to be treated like one of the herd
Daventry,
You might not be referring to my post but just in case I thought I might make my point clearer. Holding them against their will is a very dominate training method. Sort of like throwing a horse to the ground, which some extreme training philosophies use (not my thing). Holding something down or in place is fairly aggressive in a passive way. It works with calves (and even people). I thought of it because the foal is soo young and it is possible. With some young colts, it is sometimes the roughhousing that they are looking for. Most foals get away with quite a bit when they are small and usually it is not sever corporal punishment a very young foal gets from mom or the herd, otherwise there would be more injuries. Most of the time is gesturing. A wiffle bat will probably do the trick, but if he is a tough cookie, the wiffle may not work. I was just offering an alternative idea that will only work for a short time due to his size.
