[MrForbes]

I think you're probably right about it being quite difficult to do this safely with a spring.

Which is why I suggested considering using something else (perhaps compressed air?) instead....here where those folks thinking about using a spring might be likely to see it.

Anyways, if you are a team that is thinking of shooting the ball using a spring type mechanism, it might be wise to post your ideas here so others might be able to point out safety issues, or suggest other ways to do it better. My opinion is that you have little to lose by posting your designs, and a lot to gain if it helps you improve it in ways you didn't realize it could use improvement.