The only time a male horse is usually in danger of being kicked in the belly is when he mounts a mare and if that happens he may suffer an internal or external injury. A male horses penis and testicles are both in that area and horses have had their breeding careers and sometimes their lives ended by a kick. Kicking a horse in the belly is depending on the area the same as gut punching a person or kicking them in their groin. When a jockey kicked a horse in the belly on TV a lot of people complained about it and he was suspended. A mare's udder could be injured by a kick also. If you kick a horse you teach him that kicking is acceptable behavior. I have taught mine that kicking is not allowed.
We are not talking about the gential areas. A good swift kick to the belly is a very different from injuring a genital area. Also, I love my horses but when it comes to them acting dangerous, I'm going to put my sercurity first not my horse's. I'd rather injure my horse and stop a nasty, dangerous behavior than have that behavior escalate and have it end up harming myself or someone else. People come first. Not to mention horses double barrel each other quite often and often times those kicks land on the barrel area. Horses bodies are designed to take quite a bit of damage. Kicking is a dangerous, dangerous behavior that should be swiftly reprimanded by whatever means. The biggest rule for any of my horses is that they not hurt me and if they do hurt me, I'm going to do my darndest to hurt them back. If a horse kicks at me and I'm in a position to do it, I'm going to give them a good swift kick in the belly and make sure they know that is not okay.
Secondly, of course some dummy raised a fuss over a jockey kicking a horse in the gut most people see horses as sentimental beings that wouldn't hurt a fly. This is not so, if you're in a public place and smack your horse someone who doesn't know anything about horses will probably make a fuss about it. There's always someone out there who is going to disagree.
Thirdly, horses do not learn to kick because you kick. If you pick your horses nose does he then try to pick it? No he does not. When you brush your horse does he then start trying to brush himself? Nope, didn't think so. Horses immitate the behaviors of other HORSES. Not people.
I apologize for the off topic but seriously. Now concerning ICEMAN who just wants some advice. I think that as you have the facilites to do so, seperating them is the safest choice. I would however recommend being very firm with this gelding at all times, do not feed him first and do not feed him more. If possible I would make it so the two could still see each other and make a point of feeding the yearling first, wait for you gelding to calm down and then feed him. Also, feeding him more will only make him more antsy, which from your last post sounds like you most certainly realize. I think you should just set up very strict boundaries for this horse. Blue acting naughty= Blue not getting fed, obviously I'm not saying starve him but he should act calm and mannerly before getting food. You should be consistent in the way you reprimand and also in the ways you cue.