The OP does not mention what scenario he hopes to protect against. That’s an important part of risk assessment.
For example, is this about deterring a burglary? In that case, and you’re home, the burglar has guessed wrong, doesn’t really want to encounter you, and may run when he hears you. Is the scenario a “home invasion” break in? Those almost always involve armed intruders. (Often they’re wearing some kind of body armor and posing as law enforcement.) Almost all home invasion suspects are ready to deal with some resistance and will not be stopped/run away in the face of paint balls.
On top of this, if the suspects are under the influence of drugs, they may not feel or really register paint balls, or even pepper spray – at least before they hurt you.
If the scenario is a stalker-type situation where someone wants in to your residence to kill you or someone in your home, then a paint ball definitely won’t do anything.
Hopefully some of our more experienced and articulate law enforcement Dopers will contribute to this thread, but I’d like to add that the decision to own firearms for home protection is a serious one. In my two-decade policing career, for example, I didn’t get my wife a gun (and she didn’t want one) because I believe she would have a gun taken away from her and possibly used against her before she could decide to kill someone with it. Keeping the doors locked, not opening the door to people you don’t know, having an alarm system, and knowing when to run away are more valuable to her than having a gun around. And of course, I’ve always kept our guns locked up because of my children and their friends.
A good friend of mine was killed when a guy broke into his home looking for something to steal. The burglar didn’t run. He killed my friend and ran off with some tools that he sold for a couple hundred bucks so that he could buy some crack.
I once worked for a guy who surprised a burglar. He and his wife had been out to dinner. They came home, found the door kicked open, so he ran in to get his gun and got shot—with his own gun. Yes, the burglar had found it, was stealing it, and was still in the house.
Boss man survived but the lesson to me was, hey, call the cops and wait. Emotion will run high and we don’t do the safe, sane, logical thing every time under duress. He was lucky. To be fair, in those days cell phones weren’t a thing so some of the standard advice of today wouldn’t work. You’d have to go find a payphone and you couldn’t take a picture of him when he exited unless you had an actual camera with you, etc.
Always remember that any weapon you own can be used against you. Even a paint gun. I had on NPR earlier and a guy was talking about rubber bullets etc. and just because you think it won’t kill…
Did you see what a rubber bullet did to the face of Dale Murphy’s son?
Damn, maybe an inch up and he’s blind in one eye. Perfect example: you might survive it but imagine losing binocular vision (and with it depth perception).