Well folks, it's almost U.S. Open week, which means the world's best are set to embark on golf's toughest test! Knee-high fescue, slippery par putts, and demanding tee shots await the field when they arrive at Shinnecock Hills with the goal of winning the 118th United States Open.

It is hard to win any professional golf tournament, but it almost seems a bit tougher when the course is difficult and unforgiving, as is usually the case at the U.S. Open. The great champion Tom Watson once said "It takes courage to win the U.S. Open, more courage than it takes for any other tournament." Powerful words, but what does that really mean? Are there certain players who thrive in tough scoring conditions; who possess the intangible quality that keeps pars on their card while players around them crumble? That is the question this article seeks to answer.

"It takes courage to win the U.S. Open, more courage than it takes for any other tournament." - Tom Watson

Before we can determine which players perform the best in difficult scoring conditions, we first need to identify which courses and events to consider "difficult". A simple approach would be to use scoring average relative-to-par as the measure of course difficulty. However, there is an issue with that: the strength of the field. For example, if field scoring averages at The John Deere Classic and The TOUR Championship were identical, we would not conclude that the courses were the same difficulty. Because The TOUR Championship hosts a much stronger field in terms of average player quality, we expect the scoring average to be lower at that tournament holding course conditions constant. After adjusting the course scoring averages for the strength of the field that played it, we select the 10 courses with the highest adjusted scoring averages in each PGATOUR season from 2011-2017 to be in our "difficult courses" sample.

The figure below plots the raw scoring averages relative-to-par of the 20 hardest courses over the time period analyzed. You can also explore specific years in more detail by selecting a time frame to the right of the figure. To view the course scoring averages adjusted for field strength, change the selection on the top left.

Not surprisingly, the 2013 U.S. Open is the hardest event in the sample, where the field averaged 4.5 strokes over par at Merion Golf Club. Also note that 5 of the 8 toughest events from 2011-2017 were at U.S. Open venues.

Now that we have identified the most difficult courses, we want to determine who has played best at these venues. To do this, we first estimate a baseline ability level (i.e. the expected strokes-gained irrespective of the course) for every player at the time of each event in our sample. Then, we compare each player's results at these events to what we expected given their baseline ability at the time.

In an effort to weed out the impact of statistical noise, we restrict the analysis to golfers who have played at least 100 rounds at the 70 events in our sample of tough courses. The following figure shows our results: the left side shows the players who performed best at difficult courses (relative to their baseline), while the right side shows the worst performers.

We have results! Ian Poulter upped his game the most at difficult venues on the PGATOUR from 2011-2017, beating his baseline strokes-gained by an average of 0.34 shots per round at these courses. This fits with the narrative Tom Watson laid out at the beginning of the article: Poulter is known as a passionate and gritty player. Also near the top of the list are several players best known for their ball-striking prowess. This includes players like Henrik Stenson, Lee Westwood, and Sergio Garcia. These are all guys who have excelled tee-to-green throughout their careers, but perhaps have missed more than their fair share of critical putts.

On the right side of the figure, which highlights the worst performers at difficult courses, we also see some interesting names. None more so than Rory McIlroy, who is estimated to be 0.23 strokes worse per round than his baseline at the venues in our "tough course" sample. This is made even more surprising by the fact that his dominating victory at the 2011 U.S. Open is included in the analysis. Another notable on the list is Phil Mickelson. Given the reputation Phil has for taking big chances and trying to hit fairway woods out of buried lies, it is perhaps not that surprising that he is performing below his baseline at courses that are more penal. Although with 6 runner-up finishes in his career at the U.S. Open, this is a somewhat paradoxical finding.

What is the final verdict? Is there a story that can be told about all of these players, explaining the discrepancies in their performances under difficult scoring conditions? Of course not. There are several names on both sides of the figure that seem out of place (Jason Day, for example). However, by only including players who had played at least 100 rounds on the courses in our sample, we think it is likely that most of these scoring differentials do capture true differences in performance, and not just statistical noise.

Our take-home message from this blog: as you watch players battle the conditions at Shinnecock in one week's time, don't be surprised to see Poults sneaking up the leaderboard (which part of the leaderboard.. is a separate question).