First, let's look at the granddaddy of putting statistics, putts per green in regulation. Generally, when tour players hit a green in regulation they take less than two putts most of the time. Certainly at a U.S. Open where the greens are fast and difficult that tendency to take less than two putts is a little less, but still more than 50 percent of the time. To give you some perspective, the full-season average on the PGA Tour last year for putts per green in regulation was 1.781, which is about what it's been since it was first tracked in 1986. At U.S. Opens it gets a little worse, of course. For the last 20 years prior to Chambers Bay, the average was 1.877. This year, the putting average was 1.923. That's the third highest that number has been in history. Only Oakmont in 2007 (1.933) and Oakland Hills in 1996 (1.943) were worse. But these differences (less than .05 of a stroke) seem small enough to not make us worry too much.
The case for Chambers Bay's problematic greens gets a little cloudy when you look at a stat like "birdie or better percentage-putting." This number tracks how often a player makes birdie or better after hitting a green in regulation. The average last week was a birdie per green in regulation 22.4 percent of the time. That beats the 20-year average for U.S. Opens (21.3), and is better than 12 of the last 14 U.S. Opens. It almost seems respectable compared to the tour average, which generally is about 28 percent of the time.
But there are two alarming stats where the antics of Billy Horschel start to seem at least understandable: one-putt percentage and three-putt percentage. One can theorize that on superb greens, players will one-putt fairly conssitently, and at the same time, it's conceivable that on non-bumpy putting surfaces, three-putts will be less likely. At Chambers Bay, those two stats were historically bad.
The percentage of one-putts at U.S. Opens over the previous 20 years has been slightly better than a third of the greens (34.94 percent of the time). At Chambers Bay, players one-putt barely a quarter of the holes (26.27 percent). It was the worst one-putt percentage since the stat's been kept. For any event.
Finally, and most tellingly perhaps, comes three-putt percentage. As a means of comparison, the tour average for the year generally hovers around 3.00, and, of course, U.S. Opens are more difficult. But at Chambers Bay a player three-putted a relatively absurd 8.58 percent of the time. The average for U.S. Opens from 1997-2014 was 4.84. The only year that comes close to Chambers Bay's number is Oakmont in 2007 at 7.22. Chambers Bay is more than three standard deviations worse than the U.S. Open average for the last two decades. That seems beyond an aberration.
Clearly, something abnormal was happening on the greens at Chambers Bay last week. Odds are, one way or another, it won't happen again.