Four players all playing individual matches against the other 3 golfers.
Player A hits Player B's ball. Player B hits player A's ball.
Player C puts 2 balls in the water and scores a 10.
Player A and B say they can go back once they realize their error take their penalty and still have a chance to beat player C.
Player C says once they played the wrong ball he automatically won the hole.

Back to Players A and B. How do they resolve the hole?
Do they go back and play their own balls?
What happens if there is time pressure and they can't go back?
This happened to a friend and needless to say it was a cranky foursome for the rest of the round!