Your colt is like a toddler loaded up on sugar and caffine and you are trying to make him sit still and not eat the cookies and candy (grass) that he sees and not play.
It is spring time, every animal is feeling good, wants to play and wants to eat all the fresh grass. especially youngsters. He has been cooped up now for a while and he is getting frusterated. He wants to eat and play and you are what he has right now and he is trying to be the boss and play with you and make you do what he wants to do.
Make sure you have toys for him to play with while he is recooperating. That will help take out some of his aggression and energy.
When you take him out for his walk, DON'T let him eat any grass until you are done with your walk and he has been good. If he is good, he gets to eat grass as a treat.
You need to teach him some manners first before you start giving him treats.
And I agree with what Jean has said on disappline. And yes you can use a thin rope lead just like a chain and get a good effect when you jerk it for disappline but it will not cause damage a chain can. A sharp deep "NO" and a jerk on the rope and then back will get their attention.
When walking and he invades your space, you can flip the rope back behind you and smack him in the belly and a sharp NO and OVER. Or use your foot closest to him and just swing your foot backwards in his belly with a NO and OVER. Or a crop or driving whip does the same thing.
I also teach my youngsters the word over when tied. So if I am working with them, while just brushing and cleaning up or out on the lead line and I want them to move over then all I say is OVER and they move in the direction I point them.
Also be watching his movements and signs all the time so you are ahead of him when he starts thinking about doing something and are ready or try to get him to think about something else before he actually gets to do it. Like bitting, if you see him getting ready and the jerk and NO are not working. Just get your pointer finger ready and when he comes at you poke him in the mouth hard (but don't swing at him just a quick short jab) and a sharp NO and usually they will think twice the next time before doing this.
Also the more times you can take him out for exercise the better he will get because he will be burning off more energy.
Good luck!