In golf:

How big a deal is luck on the golf course? On average, tournament winners are the beneficiaries of 9.6 strokes of good luck. Tiger Woods’ superior putting, you’ll recall, gives him a three-stroke advantage per tournament. Good luck is potentially three times more important. When Connolly and Rendleman looked at the tournament results, they found that (with extremely few exceptions) the top 20 finishers benefitted from some degree of luck. They played better than predicted. So, in order for a golfer to win, he has to both play well and get lucky.

I don’t understand the statistics enough to evaluate this paper. Apparently they call “luck” the residual in some estimate of “skill.” What I don’t understand is how such luck can be distinguished from unexpectedly good performance.  If a schlub wins a big tournament and then returns to being a schlub, is that automatically luck?