While Brooks Koepka didn’t seem to be fazed by the rough at Bethpage Black—mainly because he didn’t hit many shots in it—the real challenge of the long grass isn’t that it makes the course play longer with approach shots that don’t fly as far. No, it’s that players don’t know what’s going to happen when the ball isn’t sitting on a clean lie.
The rough may be the most sinister element of Bethpage Black, and not only because it can require the forearms of a South Bronx bouncer to extricate a golf ball from its shaggy clutches. John Rae, vice president of research and development at Cleveland/Srixon, has studied the effect of rough on wedge and iron groove design for nearly two decades. The rough at Bethpage Black is the golfing equivalent of Russian roulette.
“A crisp wedge shot from the fairway might have, for example, 10,000 rpms (rotations per minute) of spin,” he said. “The same shot out of thick rough can drop that number to 2,000 rpms of spin. But put the emphasis on 'can.' One shot may have 2,000 rpms, and the next shot from nearly identical conditions could have 6,000 rpms. That variance will dramatically change how far the ball flies and what it does when it lands.”
Not only that, Rae said, but the rough can slow the speed of the club through impact just as irregularly, but almost always negatively. The effect is particularly noticeable in what’s known as the “smash factor.” That’s the ratio of how fast the ball is flying as it leaves the clubface compared to how fast your swing is. Rae said smash factor from the rough can be reduced by 20 percent or more. According to the researchers at launch monitor manufacturer Trackman, for a typical tour-level 7-iron, the smash factor might be 1.33 from a clean lie leading to a carry distance of 172 yards. Reduce that smash factor by 20 percent and you see a smash factor that’s barely above 1 and that same swing might produce a shot that barely flies 120 yards.
But it can get worse. On the first hole Thursday, Dustin Johnson hit his second shot out of the rough on the first hole only 42 yards. He used a wedge. That’s precisely the point, Rae said.
“With the rough lowering the smash factor by more than 20 percent and doubling the standard deviation on ball speed and moving even short shots offline by six or more yards, trouble ensues,” he said.
“The problem these players encounter is not that the shot has too little spin, but rather that they just have no idea what is going to happen on a shot-to-shot basis from thick rough. As the rough gets thicker, the results become staggeringly unpredictable.”
The USGA’s study of spin in 2006-07 prior to changing the rules on grooves made the case that reducing the effectiveness of groove shape basically would reintroduce this idea of unpredictability (and penalty). It showed that even with the most effective grooves the spin for even wedge shots from the rough varied between the high 3,000s and the low 7,000s. That’s pretty much the difference between a shot landing like a tee shot on pavement and, well, a wedge shot landing on a green.
The only saving grace at Bethpage Black this week might be the softer condition of the greens, Rae said. Generally, the rough could lead to less spin because the long grass gets between the club and ball. While a high shot will always roll out less when it lands on a green, a low-flying shot caused by heavy rough might also have less spin but it might not land as hot because of a more receptive green.
“On firm greens, spin is way, way more important in being able to stop the ball,” Rae said. “A ball with less spin but a steep descent angle will have a better chance stopping on softer greens. A softer green should reduce some of the end-result variability that would come from the massive launch condition variability of shots played from thick rough.”
One other perhaps obvious note of caution: Tour players who attack the ball at a steeper angle can further mitigate some of the rough’s effects. According to Trackman, Brooks Koepka’s angle of attack with a 6-iron was measured at -9.0, while the PGA Tour average is -4.1. In other words, Koepka might be more than twice as good as an average tour player. Or as Koepka might put it: Scoreboard.