No paintballs do not normally ruin car paint however, you may accidentally do that if you are not careful while cleaning it off. This is because paintballs are fired at a speed of three hundred feet per second. This speed is fast enough for the paintball paint to penetrate the car’s paint but does not permanently damage it. So, just make sure that you do not scrub off the paintball paint from the car. Use a remover or hydrogen peroxide to weaken the paint bonds before rubbing it off.