I was envisioning that in order to count as a sport as completed, one player would beat the other (and bowling/golf is just finishing it as normal). Tennis would have player one being their own doubles partner on one side of the court and player two the same on the other side, which I believe is the default for playing tennis with two players. I agree that this might work better as a category extension after thinking about it a bit more.

This would function the same as the current All Sports category, but now two players are participating, with no CPUs.