Hello Bartol,
thank you for getting in touch with us.
Generally you have to make sure that the audience as well as your team nerver is subject to any risk due to the performance. This could be solved by using a very soft and lightweight ball or a very low powered shooting mechanism. Also it could be helpfull to not shoot the ball in the direction of any person, attaching it to some kind of string or building boundaries to limit the possible shooting range.
If the ball can not be considered a safety hazard it will not be considered a projectile. To make sure this is the case for your performance we need some more information about your show. Feel free to send us technical data or a video of your mechanism as soon you have it ready.
We are looking forward to your performance!
Christian
OnStage Committee