Just thought of this one. What if your ball somehow comes to rest on a critical slope on the green. For some strange reason it stays. So the ball comes to rest. Critical slope would be one were a ball wouldn't normally come to rest. Maybe there's a slight indent it fell into.
So your in the fairway, your next person hit, his ball strikes your ball on the green. So the rule is you must replace the ball near to the previous spot. Since you were in the fairway you don't know exactly the pin point position is at. So, what happens when you try and the ball keeps rolling away because its on the slope, no matter what you do it wont stay. Wouldn't tapping the green to indent be changing the lie conditions, and be illegal. So what do you do?