I chipped my ball across the green and it came to rest in a ball size depression in the fringe, so that only approx half the ball was visible. It was either sitting in someone elses plug mark, or it was on a small sprinkler head. I had no way of telling it was a sprinkler head unless I lifted the ball. I played it as it lied, and ended up duffing it – I could only hit the top half of the ball and it just bobbled about 3ft. It was in fact sitting on a sprinkler head and as such I was entitled to relief. My question – if I suspect I’m entitled to relief, may I lift the ball to confirm (and replace it without penalty if I’m not entitled to relief)? Or is it when in doubt you just play it as it lies and suffer the consequences?

In this case you could have lifted the ball and could have inspected the area under it.

From Decision 20-1/0.7:

... if a player has reason to believe he is entitled to relief from a condition, the player may lift his ball, without penalty, provided he announces his intention in advance to his opponent in match play or his marker or fellow-competitor in stroke play, marks the position of the ball before lifting it, does not clean the ball and gives his opponent or fellow-competitor an opportunity to observe the lifting….

great – thanks Doc!