When you say “stud”, I assume you mean a piece of metal that is/was welded, or otherwise attached to the car, with threads on it so you can attach a nut?, and somehow either the welds broke or something like that and it’s allowing the stud to spin when it should be stationary? If it is like that, then it may be fairly hard to remove. If you can fit some vice grips on the stud to stop it from moving; that may help, ideally though you would want to use a welder to tack it, to keep it from moving, that is if it was like that to begin with. But as college man suggested an image would go a long way toward better suggestions of what could possibly be done.
One last thing you can possibly try, if the stud is moving between an object that has just a little bit of clearance, and it’s able to move, you could potentially take a pry bar, and use the object it is passing through like if it’s the track bar, you can use the pry bar to bind the stud to stop it from moving, while you take the nut off. This may require more than one person depending on a few things. Once you have a way to stop the stud from spinning, then you can work on how to get the seized nut off. If binding the stud, and the nut won’t come off, heat may work, but in reality unless you have an oxy acetylene torch it’s not going to do much, I’d suggest if you have a piece of metal that can allow you to hit the nut square on one side, to do that and tap it pretty hard a few times to break any rust loose, that and some pb blaster(or other penetrating lubricant) should get it off. If possible, let it soak as long as possible. Hit it a few times over the course of a day with pb blaster and it should be a bit easier to get off. Also if pb doesn’t work, CRC freeze off should.