I have very nicely asked two seperate couples (one was grandma and grandpa at the gym to watch their 11 yr old grandson play, and the other was a mom and dad duo there to watch their 13 yr old son) to please leave the gym due to a similar "NO FOOD" policy.
While we don't have signs posted in our gyms, all the coaches know the rules. Our penalty is different (County could prohibit us from using the gym - at least, that's the threat anyhow). I basically explained the policy and asked them politely and they both were "genuinely surprised" at: a). the policy, and b). that anyone actually brought it up to them and enforced it. They both complied.
Ya know Mark......I'm starting to think you attract trouble and bizarre events.....hmmmm.....NAH!
