The U.S. Open is golf’s second major championship, making it the unofficial halfway point of the PGA Tour season. Before we hit the second stretch of the year, I wanted to take a look at the metrics of some of the PGA Tour’s most popular players who have not quite played up to their potential in 2015.

Maybe one of these players will find their game this week and win their first U.S. Open (or in Graeme McDowell’s case, his second U.S. Open). And looking at the numbers, some players seem closer to playing their best than other.

These rankings are based on the 202 players who have qualified statistically for my study, and my explanations are based on my knowledge and experience working as a PGA Tour statistician.

Graham DeLaet

DeLaet is considered by some analysts to be the best player on the PGA Tour without a victory. In the previous two seasons, he proved to be one of the best ball strikers on the planet, but this year his ball striking has regressed with the most noticeable drop-off in his driving. He has a couple of issues. For starters, his club speed is down quite a bit. It was 120.96 mph in 2013 and only 117.91 mph this season. The other is that DeLaet is laying up off the tee more often, so he is effectively losing distance as he only ranks 87th in Driving Distance on all drives.

DeLaet is still fairly accurate off the tee, as he is hitting 63 percent of his fairways and he is 159th in Average Distance to the Edge of the Fairway. That’s not too terrible at his club head speed. His miss bias is only 50.7 percent to the left, so I’m not sure why DeLaet has started to utilize a more conservative strategy, as it is clearly to his detriment. He still has capable enough ball striking to limit his bogeys, but his slower club speed and more conservative nature is making it more difficult for him to hit shots close to the hole and give himself a good chance at making birdie.

DeLaet is not playing in the U.S. Open this week due to injury, and the 33-year-old’s physical issues could be a leading contributor to his woes.

Luke Donald

Luke Donald’s main issue over the years has been his driving. His strengths were just about everything else, particularly the putter and approach shots from 75-175 yards. Since that fantastic 2012 season, he has tried to make changes to improve his driving, but he has lost his superior iron play, deft touch around the greens and deadly putter.

Donald still shows some glimpses of elite performance from the Yellow Zone (125-175 yards), but his Red Zone play (175-225 yards) has completely fallen apart and his driving is some of the least effective on the entire Tour. He’s able to avoid bogeys because he still has a great short game, but a lack of distance, inferior iron play and below average putting makes birdies difficult to come by.

Donald ranks 190th and 191st in putts from 5-10 feet and 10-15 feet, respectively. This is an indicator that he may have problems with the putter that will take longer to solve.

Jason Dufner

Dufner is playing better than his earnings indicate, as he’s 46th in Adjusted Scoring Average. His game usually revolves around excellent driving and short game play. Dufner is sometimes very good with the irons and at other times he is about average with the irons. Putting is usually the weakest part of his game.

This year, Dufner’s iron play is better than it has been in the past couple of seasons, but his driving is not quite near the elite level it usually is. The same goes for his short game play. However, if his top driving form returns to form and he can make some putts, I could see him having a strong stretch of performance down the road.

Hunter Mahan

Most of Mahan’s 2014-15 earnings have come from last fall. Since then has only missed one cut, but outside of a T9 finish he has not played well in 2015.

Mahan’s strength has been his driving, and he has an underrated short game and putter. His weakness over the years has been his iron play, and he is still struggling to figure it out. When you drive it well like Mahan does and have a sound short game and putt well, it’s going to be difficult to miss cuts.

This is the similar to the way he has played in the past, and he seems to eventually have four good days with his irons game and win a tournament. It’s going to be tough for him to move to the next level with such poor Red Zone performance, but his performance this year is akin to similar to previous seasons.

So why is a he on this “disappointing” list? There’s a feeling in the professional golf world that Mahan has the skills to win more frequently, and he’s continued to fall short of those expectations.

Graeme McDowell

McDowell has made changes to his swing in order to hit the ball higher. Typically, Tour players are better off hitting the ball high than low, all other things being equal. So I can understand his desire to make changes.

McDowell’s launch angle has now improved to 11.02 degrees with the driver and his Max Height is nearly 96 feet, which is closer to the Tour average. But the swing changes have so far made him far less effective off the tee. Previously, McDowell was a perennial top-20 driver of the ball.

The swing changes also appear to have caused some growing pains with his irons. He is usually very good from the Yellow Zone (125-175 yards), but this year he’s ranked 169th. And he’s typically an elite player from the Red Zone (175-225 yards), but this year he’s only above average at 69th.

McDowell has always struggled with his short game play, and this year is no different. What is different is his Driving Effectiveness and Yellow Zone play. Combine those with a weak Short Game and it’s a recipe for making bogeys.

Phil Mickelson

Mickelson has not played poorly by PGA Tour player standards, as he is 29th in Earnings and 31st in Adjusted Scoring Average. But the 45-year-old has higher standards for his play, and since he has yet to win this season he is worth noting.

Unlike previous seasons, Phil’s driving is not doing him in. In fact, he’s more effective off the tee than the average Tour player. The difference for Phil is that his iron play, which is usually a strength, has been off a bit. The good news is that he is still good from where it counts most, the Red Zone (175-225 yards).

His short game play has been below average as well — but Phil’s Short Game is not always on point. I think he tries to hit the heroic shot too often and sometimes that costs him. If he can improve his iron play, however, then he should not have to worry about attempting the heroic up-and-down shot to begin with.

Since iron play has usually been a strength of Lefty’s, I can see him having a strong stretch of play at the end of the season.

Carl Pettersson

Pettersson is playing better than his Earnings indicate (99th in Adjusted Scoring Average). Pettersson’s game usually revolved around pretty good driving and very good putting, but he appears to have made some swing changes and that has taken a toll on his driving a little. His putting has also dipped, and he has to prepare for life without the long putter for next season.

Charl Schwartzel

Schwartzel’s iron play has hurt him in recent seasons. He only ranked 132nd on iron shots from the fairway last season, and this season his iron play has become considerably worse. Schwartzel usually has a sound short game, but has struggled around the green and has not been able to hole putts.

Adam Scott

Scott has not played in many events, so his performance is actually better than his earnings. But he is still a long ways from performing in the upper echelon on Tour. Scott is still a good-to-great ballstriker, but he has had some issues hitting approach shots from the rough. He has also been hitting the ball lower off the tee than in years past as he has adjusted to a new driver head and shaft that he switched to for more distance.

But the main issue for Scott has been his putting. Trying to transition to a traditional putter has not worked well thus far.

Bo Van Pelt

Van Pelt’s strength used to be his driver. He was a solid iron player and a bit suspect on and around the greens. He was known for hitting quite a bit up on the driver and being able to do it effectively. Now he appears to hit less upward on the driver as we can see by his ranking in Carry Efficiency.

This season he ranks 71st in Carry Efficiency (Carry Distance/Club Speed = Carry Efficiency) compared to ranking 14th in Carry Efficiency in 2012. His launch angle has only changed by 0.21 degrees since 2012, but his Spin Rate is now roughly 350 rpm lower this season. Furthermore, his hang time is less by 0.2 seconds, which is substantial for hang time.

Van Pelt is a little shorter off the tee due to the drop in club speed, but he’s missing more fairways and all things considered I think his change to a lower-spinning driver is actually working against him.