Sports Analytics Club: The Peak stat of the week

Discussing “strokes gained” as SFU golf gets ready for the 2018 season

By: Dani Chu and Matthew Ryers

With SFU golf set to begin for the 2018 season, it’s a good time to brush up on the stat that revolutionized the way we evaluate golfers. The “strokes gained” family of statistics evaluates a golfers performance against his peers, instead of simply looking at basic counting statistics. In 2011, Mark Broadie, a professor at the Columbia Business School, noticed that traditional golf statistics such as putts per green are limited as they are affected by the distance of the putt. He proceeded to develop the strokes gained metrics to account for the proximity of the ball to the hole, using newly available ShotLink data.

It is common sense that a long putt is harder than a short tap in. However, the classic metric putts per green weighs conversions of the previously mentioned shots equally. Strokes gained: putting fills this gap in our intuition by assigning values to putts based on the performance of other professional golfers from the same distance. This means that if the average number of putts to the hole in the Professional Golfers’ Association (PGA) from a specific distance is three putts and a player takes only two putts from that distance, that player will have one stroke gained putting on the field. Furthermore, if the player instead takes four shots to putt-out from the same distance they will have -1 stroke gained putting on the field.

This concept can be generalized beyond the green, to strokes gained: off-the-tee, strokes gained: approach-the-green, and strokes gained: around-the-green. These statistics, in combination with strokes gained: putting, complete the strokes gained family. Additionally, strokes gained: total measures how many shots better or worse a player is than the average player on a given day.

In order to compute the baseline number of strokes to hole out from every distance on a course, the PGA Tour uses the data captured by ShotLink. Locations are split up by distance with the green being separated into one-inch increments from the hole and all other locations being segmented into one-yard bins. From this information we can determine the distance needed to give a Tour-average player a 10% chance of a one-putt — 25 feet. These baseline averages allow us to form a coherent expectation of the number of shots it should take a PGA player to hole-out from a given distance. For example if Jason Day is about to attempt a 30-foot putt, we know it should take a PGA Tour average golfer roughly two putts to hole-out. With this information we can understand before a shot takes place what Jason Day needs to do to separate himself from the field.

Dustin Johnson, Master’s Green Jacket winner in 2016 and current number one in the Official World Golf Ranking, is known for his powerful drives and not so much for his putting. His strokes gained: putting statistics reflect that as he is the 52nd golfer in this metric with a strokes gained: putting of .382 on the PGA Tour this year. However, Johnson is ranked second in strokes gained: tee-to-green where he gains an average of 2.175 strokes compared to the field. By breaking golf into these distinct areas with the strokes gained family of statistics, we can better identify the strengths and weaknesses of Johnson. These statistics, however, go beyond the professionals and can be used by anyone. So be sure that next time you hit the fairway to measure every putt!