Strokes Gained: The Best Way to Analyze Golfing Performance

The Stats homepage for PGATour.com

Write about what you love. Writing can be a painful, laborious exercise, so if I were to attempt to prattle on for 1000 or so words about, say, fashion, or Hallmark Christmas Specials (I refuse to call them ‘films’), or the finer points of wall painting… I’d probably fall asleep midway through the first paragraph and thus not have any articles to publish. Thus, for my weekly Medium articles, I’ve tried to write about my hobbies and interest, as peculiar as some of them may be: Tetris, Scrabble, NFL… and now, golf! Is golf a sport, or a game? The philosophical debate rages on, but I definitely put it in the “sport” camp. The main acts of the game involve rapid physical movements, where strength and flexibility are assets. Plus, you move around a lot! 18 holes equals about 8 miles of walking, assuming you don’t use a cart. By sheer distance traveled on foot, golfers make other athletes look like indolent sloths. Soccer players and long-distance runners excepted, of course. I love golf, even though I seem to play it less and less, and coincidentally, I get worse and worse… which makes me less and less apt to play it… what a lovely cycle! Hey, at least I count all my strokes.

As a result, my main medium for experiencing golf is through the TV screen, watching the pros on the PGA Tour. I’m a big fan of stats and number, so naturally, I like to delve into PGA Tour stats as I watch, to see how players are doing and to try to figure out who’s going to win. Golf statistics have improved tremendously over the past 15 or so years. In the past, the metrics were super simple:

  • Driving distance (how far does a player hit the ball off the tee?)
  • Driving accuracy (how often does a player’s drive end up in the fairway?)
  • Greens in regulation % (how often does a player’s approach shot settle on the green?)
  • Putts per round (how many putts does a player hit on average, over the course of a round?)

These statistics, as simple as they are, are far better than nothing. However, they often give an incomplete picture. Obviously, driving the ball farther is better, and hitting it in the fairway is better, ceteris paribus. If Player A averages 280 yards off the tee with 75% accuracy, while player B averages 300 yards with only 60% accuracy, who is better? With just those two numbers, it’s hard to say.

Likewise, if A hits the green 80% of the time, but leaves the ball 45 feet away on average, while B hits the green 70% of the time, but averages 25 feet away, which is better?

Thankfully, the PGA Tour devised a wonderful methodology for measuring player performance: Strokes Gained.

Current Strokes Gained Top 10… Tiger Woods is nowhere to be found!

Basically, SG amasses every shot hit by every player in every tournament. Seriously! That comes out to an average of, roughly, 150 * 3 * 70 * 40 = 1,260,000 shots per year. 1.26 million! The Tour takes this data and uses it to model how players perform from a given distance and situation. For example, with the ball in the fairway from 180 yards away, players usually finish in about 3 strokes. So if a player hits the ball onto the green from 180 yards away and makes their birdie putt, thus finishing in 2 strokes, they have “gained one stroke on the field”. I.e. they have outperformed the average PGA Tour golfer by 1 shot from that scenario.

For putting, PGA Tour golfers make 7'6" putts about half the time, hence they miss half the time. Thus, the expected number of strokes from 7'6" is: 0.5 * 1 + 0.5 * 2 = 1.5. So if a player makes a 7'6" putt, they have completed it in 1.0 strokes and have “gained” 0.5 strokes compared to the “field” (average PGA player).

As you can see, this way of breaking down each and every stroke, and comparing a player’s shot to how the average player would have done from that scenario, gives a far clearer picture than just counting putts, measuring drives and checking whether or not a player hit a fairway or green. Let’s go through an entire hole as an example:

Actual PGATour.com screenshot — this shows the play-by-play for Kevin Na’s 18th hole

A given par-4 of 490 yards averages 4.25 strokes. Player A is up.

  1. Tee shot travels 300 yards and settles in the rough, leaving him 200 yards away in the rough. On average, PGA Tour players take 3.4 shots to finish a hole from 200 yards away in the rough. A’s expected score on the hole is now 1 (the number of shots actually hit) + 3.4 (expected further shots) = 4.4. Hence, the player has “lost” 4.4–4.25 = 0.15 strokes after his drive, so his Strokes Gained Driving = -0.15.
  2. The approach shot, from 200 yards in the rough, settles on the green, 45 feet away. On average, PGA Tour players take 2.1 shots to complete a hole from 45 feet on the green. A’s expected score is now 2 actual shots + 2.1 expected shots = 4.1. This is an improvement of 4.4–4.1 = 0.3 shots. Hence, based on this fine approach shot (hitting the green from 200 yards away, out of the rough, is a tall order even for professionals!), A’s Strokes Gained on Approach = +0.3. His overall performance from “tee to green” is -0.15 + 0.30 = 0.15.
  3. Starting from 45 feet away, the player hits his first putt next to the hole and taps in for a par 4. Since his actual # of strokes was 0.1 lower than expected (2.0–2.1), A’s Strokes Gained Putting = +0.1.
  4. Thus, the breakdown looks like this:
  • Strokes Gained Driving: -0.15
  • Strokes Gained on Approach: +0.30
  • Strokes Gained Putting: +0.10
  • Strokes Gained Overall: +0.25

In the past, an analyst would have said “Player A missed the fairway, then hit the green, then hit two putts”. But thanks to the massive amount of data possessed by the PGA Tour via its ShotTrack technology (which, believe it nor not, Ripley, tracks shots), we can get a super detailed picture of every single player’s performance in all the different areas of golf: driving, irons, chipping, putting… sadly for weekend hacks, the Tour doesn’t keep track of gimmies, mulligans or the beloved foot-wedge, which is the best club in most players’ bags!

Conclusion

I apologize for this jargon-laden slog of an article which, to anyone other than a golfing and PGA Tour fanatic, must be about as interesting and entertaining to read as watching paint dry, and then watching said dried paint crack. I should have put a “TRIGGER WARNING: EXTREME GOLF AND STAT NERDDOM BELOW. CAVEAT LECTOR”. I’ll make sure to do it in the future.

My next article will feature two of my favorite subjects: golf and simulation. Ideally, we’ll be able to figure out a player’s chances of winning, given the leaderboard and how many holes are left to play. Should be a nonstop roller-coaster thrill ride. Until next time!

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