The only problem, as I understood is the 3rd party service that requires excessive amount of personal data, right? The system of booking time slots on courts is absolutely normal both for clubs courts and public ones, and it is the only solution that works when you want to provide access to many people for something valuable such as court. Without it no one can have guaranteed access to courts … As for data, I suppose considering malicious actors that easily can destroy public good, at least name and phone is required.