Sure - apart from Water Hazards - any where you like and for any reason, its your decision no-one elses.

So that includes out in the open on the fairway if you want, let alone when up against a tree.

The oft quoted example is when you mis hit your putt and it rolls off an elevated green and down the slope into the fairway twenty yards away - rather take on a possibly tricky little pitch you are entitled to declare the ball unplayable and take the putt again.

Costs you a penalty and your friends might not like it but hey sometimes the rules can help!