It's a cross between the ones fighting and playing. A lot rougher.
My buckskin runs from them. When he gets cornered, he'll turn and kick but not hard.
The ones I'm worried about are the newer horse and Draft. The newer horse will continue nipping at the Draft until he stops eating and starts raring up. In the last few days, the Draft has started chasing him down because he'a tired of the aggravation
3 of the horses are 3-6 years old and the Draft is about 8-9.
Other more experienced people I have a theory but I don't want to say try it to the OP, what about short interaction times? I imagine it would be possible for the newer (young) horse to just be too full of himself and just pestering the others to the point they just can't take it. What about doing daily interactions? Possibly making sure the said horse is worked before interaction either through riding, active lunging, games...something interactive. Then let the horses interact for an hour or two then separate again?
That way so this new horse can learn to interact with the new horses when he has expelled his energy and when the current horses are more tolerant because they haven't been bothered for hours on end. This could all be supervised to make sure nothing would escalate. Most of it sounds like a pesky youngster that is getting on the senior's nerves and stressing out the others. I'm thinking full separation just may cause the horse to become more unsocial.