Over the past 2 years, Xander Bogaerts has been one of the best offensive shortstops in the game. After breaking onto the scene for the Red Sox 2013 championship run, he had a tough rookie year in 2014. However, Bogaerts was a top offensive SS in both 2015 and 2016, posting .320/.355/.421 and .294/.356/.446 slash lines and WRC+ of 111 and 115. Considering he just turned 25 years old, Red Sox fans expected him to take another step forward this year and be part of a collective effort to replace David Ortiz’s bat.

Instead, he took a step back this year, posting a slash line of .273/.343/.402 and WRC+ of just 95. By any metric, he’s been worse offensively in 2017 than in 2015 and 2016. While his production hasn’t been abjectly terrible, for a player with as much potential as Bogaerts, one would expect progression as opposed to a step back in production. I decided to dive into Statcast data to try and understand if the data could help explain why Bogaerts has taken a step back this year. Going into the research, my hypothesis was that his right wrist injury has been lingering throughout the season and significantly affected his output at the plate.

After being plunked on July 6th, Bogaerts acknowledged that the injury has lingered with him throughout the season. To illustrate, he sat out a pivotal series with the Yankees in early September – nearly two months after the initial injury.

My first thought was to look at his plate coverage and compare it to his three previous years in the MLB, specifically 2015 and 2016 when he excelled. Has his approach been markedly different due to his wrist injury or any other factor? Below is a density plot of the location of every pitch Bogaerts has hit in his career, broken out by year. The plots are from the catcher’s perspective (i.e., Bogaerts, as a RHB, is positioned on the left side of the graph).

Figure 1 - Bogaerts' hits over time

Looking at the plots above, the most striking observation comes from the inside third of the plate. When compared to his stellar 2015 and 2016 seasons – in 2017, Bogaerts has had much less success getting hits on the inside part of the plate. The question is – why? I believe his wrist injury has caused this lack of success on the inside third of the plate. More so than any other pitch location, the ability to hit the inside pitch depends on a hitter having quick wrists to get the bat head around quickly to square the pitch up. It makes sense that his bat speed has been affected by a wrist injury, thus explaining his lack of success on inside pitches. Additionally, the focal point of his hits is on the outside third of the plate, as opposed to a more centralized spread the past two years, indicating his success has been concentrated in one area.

After looking at where Bogaerts has been successful, I decided to break out where he’s been unsuccessful. Unsuccessful here is defined as a swinging strike or contact for an out. While these plots do include some element of luck due to BABIP, it does provide a reasonable approximation for understanding where Bogaerts has struggled.

Figure 2 - Bogaerts' outs and misses over time

Looking at this set of plots, what stands out to me is that Bogaerts has been much more prone to "chasing" pitches low and away this year when compared to 2015 and 2016. The density of outcomes outside of the strike zone low, away, and low and away is much more dense in 2017 than in ’15 and ’16. This is also proven out by his jump in K% in 2017, 18.3%, a career high. This could be a cause of having to change his approach to be more aggressive on outside pitches, knowing that he doesn’t have the bat speed to be successful on the inside part of the plate.

Now that we’ve established Bogaerts lack of success on inside pitches and his tendency to chase low and away, I then thought it would make sense to dive into pitch-specific outcomes. We know where he has struggled with pitches, but has he struggled with any one pitch specifically? Below are pitch outcomes broken out by pitch type, along with the number of pitches he saw in each season. While every pitch type was evaluated (including the rare Eephus), I’ve only included three of the pitches he faced most – 4 seamers, sliders, and curveballs.

In the tables above, I took the average outcome rates for 2015 and 2016 to provide a baseline in which to compare against. I then took the 2017 outcome percentages and compared against the baseline to see if anything stood out. What I found most interesting is Bogaerts’ performance against 4 seamers this year. He’s experienced a drop in hit rate and foul ball rate, along with a marked increase in called strikes and misses / outs. A drop of nearly 33% in hit rate for 4 seamers, the pitch he sees significantly more of than any other pitch, shows that this has been the problem pitch for Bogaerts this year. When we look at other pitches, like the slider and the curveball, we see that he has been better against the slider this year and markedly worse at hitting the curveball. However, the bulk of the issue this year has been with the fastball due to the pure volume of fastballs faced relative to any other pitch type.

This finding again corroborates the fact that Bogaerts’ wrist has been a significant factor in this season’s performance – a wrist injury would prevent him from squaring up pitches in the mid to upper 90s due to his impaired bat speed. It could also cause him to lay off more fastballs, knowing that he can’t catch up to them, leading to the increase in called strikes.

Ultimately, the Statcast data shows that in 2017, Bogaerts has shown the following deviations from his 2015 and 2016 seasons:

1. Inability to get hits on the inside third of the plate

2. A tendency to chase pitches low and away,outside the strike zone

3. Substantially worse performance on 4 seam fastballs, the pitch he faces most often

In addition to the research performed, looking at Bogaerts’ exit velocities by both pitch type and plate location may help further prove the conclusions reached or shed new insight. Additionally, it would be interesting to look at # of pitches thrown within quadrants both in and out of the strike zone, to see if the way pitchers have approached him could be the cause for some of his struggles.

Despite what the data has shown, there is reason for optimism that Bogaerts has finally put his wrist issue behind him and will be able to get back to his old self in the playoffs. From September 11th on, the date where returned from rest to heal his hand, Bogaerts has slashed .307/.422/.440. While this is a small sample to be sure, it is an encouraging sign heading into the ALDS – especially his 3 run HR against the Blue Jays that came against a 4 seamer on the inside third of the plate.

Kevin Hisey is a MBA student at the University of Southern California. Upon graduation, he is looking for a job that combines his passion for sports and data. He can be reached at Kevin.Hisey.2018@marshall.usc.edu