Many basic rules of tennis are ignored. For example, at one point, Jimmy Pelton is shown serving, but is standing well inside the court, meaning he would be foot faulted.
When the gang chases Anthos after having seen him when they arrived at Jimmy's mansion, Daphne runs with her arms out in front of her, as though she is trying to grab something.
Wimbledon Tennis Club is depicted as a single stadium in the middle of open country. In reality it is a large tennis complex in a London suburb, with dozens of courts, bounded on one side by a large park and golf course, and otherwise surrounded by housing.
Why would Anthos attack some visitors (Shaggy and Scooby), but not Jimmy himself?
Jimmy doesn't seem to realize that he's wearing Velma's glasses, which must mean that their prescriptions are identical...which, while possible, is extremely unlikely.