That's just crap. I coach but that doesn't matter. I also am on the board of my neighborhood's HOA. I'm not claiming to be an expert on City ordinances and zoning laws, but they would have had to let your coach know what he was in violation of. If there was no code that covered it; they could ask all they want and he could tell them to FO & D.
I've made drop in's off of my roof and even a jump on the roof with a landing hill in the back yard. My neighbors just made a tow in jump in their front yard a few days ago when we got a storm. We've never had a problem.
Tell your coach not to cave so easy. A back yard setup is like a jungle gym for big kids. It would be like the City telling someone that they couldn't put a kiddie slide in their backyard for their children.