Rough Estimate: The real effects of Erin Hills' tall grass
The rough at Erin Hills seems to look nastier than it seems to be playing, and that would seem to violate one of the USGA’s long-held U.S. Open tenets for the infamous “cost of rough” penalty.
Traditionally, hitting the ball in the rough at the U.S. Open has resulted in players who hit their tee shots into the rough scoring half a shot or more over par on that hole. The USGA even keeps a statistic on the subject, called “cost of rough,” and that number works out to be between .45 and .55 of a stroke at a U.S. Open.
Players went into Erin Hills this week so wary of the rough and so vocal in their collective wariness that they were likely relieved that the USGA cut back some of the thigh-high fescue lining some of Erin Hills fairways before play began. What’s resulted thus far is a near record number of under-par scores in U.S. Open history.
But that doesn’t mean the rough has been a pushover. According to the USGA, the cost of rough penalty at Erin Hills this week has been .601, or higher than the usually sought-after half-stroke penalty, and nearly 50 percent higher than last year at Oakmont. Of course, driving accuracy is higher this week at Erin Hills than at a typical U.S. Open. Of the players that have made the cut, the fairways hit percentage is a staggering 78.2 percent. It was 56 percent at last year's U.S. Open at Oakmont last year, and the current PGA Tour average is 60 percent.
But what does the so-called cost of rough really mean in terms of the rough’s impact on what happens to the golfer, the golf ball or the swing? Well, as sure as the USGA is about the intended effect of missing a fairway, the world of those who study the technology of golf are less certain.
“We’ve tried to run finite element simulations where we model the turf and actually simulate the club going down into the turf,” said Evan Gibbs, Callaway’s senior director of research and development for metalwoods. “There was not a ton of success.
“It’s very, very challenging, and part of it is just the variability. The material models for the different kinds of soils and grass takes quite a lot of computational power to handle something like that.”
You see, not only is it difficult to simulate rough and its effects (which range from shorter-than-usual distances to low-spin “flier” shots that can travel 20 yards farther than a standard distance), it’s also difficult with any certainty to simulate how a player might react or modify his swing for a shot from the rough.
“It totally depends which club, which player and how thick the rough is, the last of those being the biggest effect,” said Paul Wood, vice president of engineering at Ping.
Wood said he has run a number of actual player tests of shots being hit from the rough. Looking at those results, he believes swing speed might be reduced by 10 miles per hour for shots from thick rough like you would find at a U.S. Open. In one test, he measured 7-iron shots and saw a decline of 15 miles per hour of ball speed, a 2,500 rpm reduction in spin, and 25-yard shorter carry distance. Wood said a test with a 60-degree wedge saw less effect on ball speed, but a greater effect on spin, an average of 6,000 rpm less spin even in light rough, which is more than half the spin typically generated by a 60-degree wedge shot.
But here’s the thing: The effect of rough might even be greater than that. “When we did a test asking players how they swing when the ball is in the rough, most players said they swing faster and many said they try to be steeper too,” Wood said. In other words, players might be swinging faster and still losing 15 percent of their distance.
On the PGA Tour this year, players are a combined 516-over par on shots from the rough, which sounds like a lot until you factor in that total is based on 7,254 attempts. That’s not even one-tenth of a stroke of a penalty.
So what does all this theorizing mean for you? Wood says keep it simple should you stray from the short grass: “If it helps the average golfer think ‘I should probably take an extra club from the rough,’ that would be a good thing,” he said.