Quidditch is a fictional sport featuring 'two teams of seven players riding flying broomsticks, using four balls and six elevated ring-shaped goals.' Mere mortals have taken to playing a version without the flying. Here's a story about it from the now-defunct NPR show 'Day to Day.'
The person who bails the Mayor out with the correct pronunciation is none other than his Parks Commissioner, Adrian Benepe. He has good reason to know. His son, Alex Benepe, is the president of the National Intercollegiate Quidditch Association (and appears in the 'Day to Day' story).
But lest one think that the Parks department is playing favorites by creating a brand new Quidditch field without sufficient demand, it turns out that Potter fans have been playing monthly games in New York for quite a while, most recently in Greenpoint's McCarren Park.