Startup Idea : Find buddies for sport and outdoor activities

I would like to see an app that helps you to find people in the area to do sports. Example: New in a new city and you have a tennis court around corner. Post the place and time and people who are signed up will get an alert and can contact you. Obviously works the same way for a volleyball game at the beach. I have a lot more ideas regarding this app, but waiting for feedback first.