Theorizing DeJong's Second Half

Before the season started, I had Paul DeJong as my personal pick to shock everyone in 2019. Honestly, I even thought he would outperform the then-newly acquired perennial All-Star, Paul Goldschmidt. I primarily went with this prediction for two reasons: his underrated defense and injury-stifled offense. Often overlooked, DeJong’s defense in 2018 was good enough to win a Gold Glove in any year Nick Ahmed wasn’t having his own breakout season. Offensively, DeJong was still performing above average too, even after he fractured his hand on a hit-by-pitch in the middle of the season. With his past working alongside him, I felt his third season in the majors had all the signs pointing toward a breakout year in 2019.


That didn’t exactly pan out.


Of course, that’s not to undersell his 2019 season, as he did end up leading the Cardinals position players in fWAR (4.1) — and he would have likely eclipsed 5 fWAR had he even been an average hitter in the second half of the season. DeJong’s offensive season seemingly fell apart from mid-May to the end of the year, so what happened? I have four major theories, but before I get there, we should first take a look at how well DeJong did before things went awry.

On Opening Day, DeJong didn’t get off to a blazing start per se — going 0-4 with three strikeouts. After that game, though, he wouldn’t strikeout over 3 times in a single game for 66 consecutive games, the longest such streak of his career. From Opening Day to May 19, DeJong carried a .320/.408/.562 slash line and a 0.621 WPA (win probability added). Yes, those were the numbers he was producing. Of course, anyone can get hot for a few weeks and it wasn’t a sure sign that things would stay that way. Besides, he probably just got extremely lucky during that time period, right?


Actually, not really. That was my first thought too.


On May 19, DeJong had a .406 xwOBA (around 100 points above league average), a .306 xBA (around 60 points above league average) and a .544 xSLG% (around 150 points above league average). He wasn’t exceptionally lucky, but he was on the road to a simple diagnosis: DeJong was forming a breakout year. His defense remained at a Gold Glove caliber and his offense had hit its peak. By the beginning of May, he was as good as anyone in the league, finding himself ranked second in fWAR in the NL, trailing only soon-to-be MVP Cody Bellinger. Suffice to say, this was an impressive start — but what happened after this? What caused his sudden and rapid downfall? Let’s theorize.



Theory I: Did The League Adjust To Him?


This could make a lot of sense, especially when you consider his spike in strikeouts. From Opening Day to May 19, DeJong had a 16% K rate. However, from May 19 to the end of the year, that number jumped to 25%. This could be explained away if pitchers pitched him differently — and if they picked up on a weakness, they would be smart to expose it. Is that what happened? It’s difficult to pinpoint exactly what changed, but here are some numbers to explore. Specifically, the following are the pitch-type% DeJong faced in the first three months.




As seen above, the only substantial change within the first three months is the offspeed% from May to June, which is in line with when he started to lose his edge. It also makes plenty of sense when you look at his expected stats for pitch-type% by month. In April, DeJong had a .695 xSLG% on fastballs and a .668 xSLG% on breaking pitches. How about offspeed? A staggeringly low .347 xSLG%. Pitchers clearly figured this out and decided to throw him a lot more offspeed pitches. In a perfect world, our hunt for a clear-cut answer would end there, but unfortunately, it’s more complicated than that, because if we continue just one more month, we get this:




If you’re keeping score at home, pitchers essentially went right back to their game-plan from April and May, but DeJong still struggled. This doesn’t necessarily mean that the league didn’t adjust to him, but if they did so it likely wasn't connected to the pitch-type% he saw when he began to struggle. I’ll touch on this again later, but for now, let's move onward.


Theory II: Was DeJong Overworked?


Yes. Absolutely. I don’t really think this one is up for debate, but if you need some numbers to back up that theory, I’ve got you covered. The most obvious thing to point out would be his games played total for the year: 159. That only leaves 3 games in the entire year in which he did not play. Let’s find those 3 games, shall we?


- March 28th - April 3rd (6 consecutive games played)

- April 4th (off day)

- April 5th - June 9th (57 consecutive games played)

- June 10th (off day)

- June 11th - July 7th (24 consecutive games played)

- All-Star Break

- July 15th - August 28th (41 consecutive games played)

- August 29th (off day)

- August 31st - September 29th (29 consecutive games played)


In my opinion, this kind of managing can only hurt players and the team as a whole. I can understand not wanting Yairo Munoz to start for you at shortstop, but after the call-up of rookie sensation Tommy Edman in early-June, time could have easily been made for DeJong to rest his feet a bit. Now, by no means was DeJong the only player that was overworked in 2019, but his case is likely the most egregious one.


So yes, a lack of rest was almost definitely a contributing factor to DeJong’s extended slump, but I’m not confident in saying that it was the sole contributor. Let’s keep going.


Theory III: Is This Just Who DeJong Is?


In his short career, DeJong has garnered himself a reputation for being streaky at the plate. But is it fair to say that he was just stuck in a massive slump for four months? Well, there isn’t a plethora of statistics I can throw out there to gauge whether it was just an elongated slump or not — but we can look into his history of slumps and streaks and use them as a comparison with what he was experiencing this season.


When we look back at his rolling xwOBA in 2017 and 2018, we can start to notice a consistent trend: inconsistency. Prior to his 2019 campaign, his longest slump — which I will identify as having an xwOBA below league average for 25+ PA — was about 72 PA between August 21st and September 10th of 2018. During that span he had a .702 OPS. For comparison, his longest slump this year lasted around 189 PA in which he had an abysmal .612 OPS. This kind of cold streak was unprecedented for DeJong. So, if none of his previous slumps can compare to the one we saw this year, what about his hot streaks?


DeJong’s longest hot streak — which I will identify as having an xwOBA above league average for 25+ PA — prior to 2019 was about 77 PA between August 12th and August 31st of 2017, his rookie season. His blazing hot start this year lasted around 216 PA. While those hot streaks are not similar in length, they’re very similar in production. In the 2017 streak, he had a .306/.351/.528 slash line, while in 2019 the hot streak resulted in a .296/.398/.515 slash line. Aside from the OBP, they’re eerily similar. So then, maybe this is the key? Maybe he just caught fire for longer than usual and it was nothing more than Paul being streaky? Sure, that’s a valid theory. However, it still doesn’t explain why his production dropped off without warning for the rest of the year, which brings me to my final theory.


Theory IV: Did DeJong Reinjure His Hand?


On May 22, in the first game of a double-header against the Royals, DeJong was hit by a pitch.


gif courtesy of @VanHicklestein



As you can see here, it hit squarely on his right wrist. Ouch. At the time, there was no indication that he was injured. In fact, not only did he continue to play until being removed in the 7th inning, but he also played all 9 innings in the second game of that same double-header. There really was no cause for concern. However, looking back, this hit-by-pitch sticks out. If you look for an exact date that you can point to and say, “That’s when DeJong went cold,” you’d be looking between the dates of May 18 and May 22.


For curiosity’s sake, how about his numbers from May 22nd to June 6th? This is where it gets depressing. In those 13 games, DeJong had a .091/.231/.159 slash line with a .278 xwOBA (32 points below average). The reason for these seemingly random dates is to show that immediately following this HBP, DeJong started to dip rapidly. Now, it should be noted that the wrist in question was not the one fractured in 2018, although it would seem to me that any injury to a wrist, fracture history or not, could result in an offensive plummet.


I want to be clear that I am not accusing anyone of forcing DeJong to play through an injury, nor am I accusing DeJong himself of doing so, but it wouldn’t be the first (or last) time that a player has done just that. As anyone who has played the game will tell you, nobody is 100% healthy by the end of a full season.


Conclusion:


In reality, it could be a combination of these things. The league could have adjusted to him in some fashion that is too complex for me to find myself (such as pitch sequencing), and DeJong could have fallen into a slump that took place around the same time that he suffered a nasty hit-by-pitch on his wrist. Then, to make a bad situation worse, he wasn’t given time to recover from the injury. A perfect storm of bad luck, so to speak.


It also could have been none of these things.


Sometimes in this game, things happen that can’t really be explained. There are a million possibilities, but the truth is that we will likely never know the answer to what really happened this year. All we can hope for is a healthy, impactful year for DeJong, both for his sake and the Cardinals’. I, for one, am excited to see what’s in store for Pauly next year. Here’s to another All-Star campaign in 2020, and here’s to giving him one more chance to live up to my high expectations from a year ago.



All data referenced was provided by FanGraphs, BaseballSavant or BaseballReference

Cover art and pitch-type% graphics by @cardinalsgifs

Gif provided by @VanHicklestein

Edited by @joelchulsey