It's called "rearing" not "raring" or "rear" opposed to "rare"
It's a way for him to avoid your authority.
When my young colts have pulled this, I usually follow as instantly as possible with a loud squeal and forcing him to back up for a long time, and shank him (tug downward on his lead rope/halter, no chain) down just as we begin moving back.
Most of my stallions already know to stay out of my space, so for me to advance towards them is for them to back up. If yours doesn't know this, he won't understand anything, and so you have to establish some basics in order to curb this dangerous behavior.
If you're uncertain about handling a stallion, it might be a good idea to get a trainer or experienced handler to help you. It is not necessary to HURT a horse to discipline them, even a "bad" stallion. They don't know what you want from them, and a stallion's job is to challenge and work/assert his authority.
For me, watching herd interaction is a big help, and if I'm meaner than his meanest mare, I almost always have the upper hand.
It can be a constant job to keep a stallion in line, but some of them "get it" and don't do much in the way of challenging, I would never say a stallion is 100% fool-proof in his manners just because something may arise that gets him feeling defensive and puts him in hormone-driven instinct response.
Anyway, I hope this helps some. Hard to know how to help w/out seeing the behavior, but some ideas just to get you thinking about it, hopefully, and good luck w/him!