Tennis would be a good project, the AI is pretty straightforward, and you only have 2 characters and a court so there's plenty processor power for graphical touches.
Skateboarding is very difficult to program, probably the most difficult, considering that Tony Hawks is the only skateboarding game series that worked. 2-on-2 basketball is a consideration too.
Try and pick a sport that you can make a good job off in DBPro, like only a few players. Maybe 3-on-3 street hockey would suit you - the AI for a fast scoring game like hockey is pretty straightforward too.
Van-B
The nature of Monkey was irrepressible!.