‘Carter Kieboom: Starting Third Baseman’, An Optimistic Take
Just forty-two days after playing a key role in helping the Washington Nationals win their first World Series in franchise history, free agent third-baseman Anthony Rendon signed a 7-year contract with the Los Angeles Angels worth $245 million. This left the Nationals with a hole at third base the size of 7 fWAR.
If re-signing Rendon was Plan A, then Plan B went out the window when the news broke that Josh Donaldson would be joining the Minnesota Twins in 2020. So the Nationals pivoted once again, to 22-year old Carter Kieboom, according to Davey Martinez.
Of course, the Nationals have been connected to names such as Kris Bryant and Nolan Arenado, who could be potential trade targets for the remaining days of the offseason. For the purposes of this article, though, we will be assuming Carter Kieboom will be the Nationals’ starting third basemen heading into the 2020 season.
Major League Experience
Kieboom made his major league debut on April 26th, 2019, and played eleven games before returning to Triple-A Fresno for the rest of the season. To put it politely, his major league production was less than desirable. During those eleven games, Kieboom came to the plate 43 times, slashed .128/.209/.282, with a 17 wRC+ (yes, 17), and a -0.5 fWAR.
As expected, going from a superstar third baseman who finished third in MVP voting the year before, to an unproven rookie whose lone time with the Nationals wasn’t exactly smooth sailing, has left some fans a bit uneasy.
So, is concern over Kieboom based on his limited big league experience warranted? The easy answer is no, absolutely not, a sample size of not even 50 plate appearances means pretty much nothing. But there might be some data within those plate appearances that provide us with reason for optimism, and we’re going to take a look.
Disclaimer: Before digging deeper into these numbers, it needs to be made clear that 43 plate appearances is a ridiculously small sample size and any statistics resulting from this sample hold no legitimate predictive value. The purpose of analyzing these numbers in this article is simply to figure out what went right or wrong within those specific 43 PA.
Overall, Kieboom may not have looked great during his one stint in the majors, but there were some bright spots. Namely, when he made contact, he hit the ball hard. Per Baseball Savant, over 23 batted ball events, Kieboom averaged an exit velocity of 90.9 MPH, higher than the 2019 MLB average of 87.5 MPH. He also hit the ball hard at a rate of 43.5% (MLB average was 34.5%).
The Strikeout Problem
Clearly, making solid contact wasn’t Kieboom’s biggest problem. The real problem was that Kieboom often struggled to make any contact at all. In those 43 plate appearances he struck out 16 times, good for a 37.2 K%, a higher mark than any of his previous seasons in the minors, at any level. And yet, even with all of those strikeouts, Kieboom didn’t chase bad pitches that often. In fact, his chase rate was just 21.3%, a full 7 percentage points below the major league average of 28.3% (Baseball Savant).
So if Kieboom didn’t chase bad pitches, then why did he find himself walking back to the dugout empty-handed so often? It turns out that the 21-year old wasn’t just taking pitches outside of the zone, he was taking the pitches he saw in the zone, too. Take a look at Kieboom’s Zone% and Zone Swing%, compared to the MLB average (All swing profile data courtesy of Baseball Savant):
| Zone% | ZoneSwing% | |
| Carter Kieboom | 55.4% | 47.3% |
| MLB Average | 48.5% | 66.1% |
What are these numbers telling us? Well, we already know Kieboom showed good patience at the plate and didn’t chase bad pitches too often. Pitchers, maybe seeing a fresh call-up and thus feeling more comfortable attacking him in the zone, did so more often (55.4% of the time) than they would an established MLB-level hitter (48.5% of the time).
The problem was that, instead of punishing pitchers for trying to take advantage of his inexperience, Kieboom only swung at 47.3% of these pitches in the zone. An average MLB hitter swung at 66.1%. This was more than likely a primary contributor to him striking out almost 40% of the time.
These numbers seem to suggest that Kieboom was rather tentative at the plate during his 43 big league plate appearances. Suddenly, he lacked the aggressiveness that had helped him reach the major league club in the first place.
A prospect showing some basic signs of being uncomfortable during his first few MLB games isn’t all that uncommon, and shouldn’t be too concerning, unless it persists. The idea is that, as time passes and the prospect becomes more comfortable at the dish, his true talent level will emerge. In fact, there’s recent precedent for this in the form of a player currently on the Nationals’ roster.
The Nationals Have Seen this Before
The player with whom Kieboom will be sharing the left side of the infield in 2020 had the same problem when he was first called up. Let’s revisit that table, but this time include Trea Turner’s numbers from 2015:
| Zone% | ZoneSwing% | |
| Carter Kieboom (2019) | 55.4% | 47.3% |
| Trea Turner (2015) | 57.9% | 54.5% |
| MLB Average | 48.5% | 66.1% |
For context, Turner was with the Nationals for 27 games in 2015, but had just one more plate appearance during that time span than Kieboom has had, 44. We’re dealing with very similar sample sizes.
Just like Kieboom, 2015 Trea Turner also saw pitches in the zone at a higher rate (57.9%) than the average MLB player, and he too swung at those pitches at a much lower rate (54.5%) than the average MLB player. And what were the results? A slash line of .225/.295/.325, a 72 wRC+, and the highest K% of his professional career at 27.3%. In other words, pretty bad.
So here’s the real question, did Turner adjust? The answer, as we all know, is yes. In 2016, his official rookie year, Turner came to the plate 324 times and slashed .342/.370/.567, with a 146 wRC+ and 3.3 fWAR. He finished second in Rookie of the Year voting. Now, let’s add one more row to our table, and see if Turner’s aggressiveness towards pitches in the zone changed at all from 2015 to 2016:
| Zone% | ZoneSwing% | |
| Carter Kieboom (2019) | 55.4% | 47.3% |
| Trea Turner (2015) | 57.9% | 54.5% |
| Trea Turner (2016) | 49.2% | 63.4% |
| MLB Average | 48.5% | 66.1% |
And there it is, the adjustment we’ve been looking for. In 2016, Turner saw pitches in the zone at a lower rate (49.2%) than he had in 2015, but he swung at them much more often, 63.4% of the time — up by nearly 9 percentage points from his 2015 mark! The results of this adjustment speak for themselves; Turner was 46% better than the average major league hitter in 2016 according to wRC+.
This, of course, was not the only reason Turner improved so much in 2016, but it’s hard to deny that it was a serious contributing factor. The increased aggressiveness has certainly stuck; his ZoneSwing% sits at 64.6% over the 4+ seasons of his career.
So, in 2015, the Nationals called up their top prospect for 44 plate appearances. He struggled at the plate, taking too many hittable pitches in the strike zone, resulting in the highest K% ever seen from that prospect. — Sound familiar so far? — However, the next year, the prospect started attacking those hittable pitches, and ended up posting the second-best wRC+ on his team. This is the part that the Nationals hope Kieboom can emulate.
Now, there’s no guarantee that he will do so or that it will turn him into an elite major league hitter, but it seems like a good place to start. If he does accomplish this, we could also see other strengths of his offensive game that weren’t as prominent in 2019 thrive once again.
Batted Ball Data
When taking a look at Kieboom’s career batted ball profile, it becomes clear that he’s always been a pull-heavy hitter. In four minor league years, he has only pulled the ball less than 40% of the time once, and that was 39.8% during the 2019 season. Throughout most of his professional career, Kieboom has yanked somewhere between 45% – 55% of his batted balls to the left side of the field. It seems like it’s been working for him too, since he has a wRC+ of 131 in the minor leagues.
Even though Kieboom’s time with the Nationals in 2019 didn’t see him pull the ball nearly as much as he normally does (26.1%), the results he got when he did were, for the most part, very good:
- Home Run
- Single
- Single
- Ground Out
- Line Out
- Ground Out
So, given more plate appearances, it’s likely that Kieboom’s batted ball profile will adjust to more closely reflect what it has been throughout his professional career, and with it will come better results.
It’s also likely that an increase in aggressiveness, as was previously discussed, will allow Kieboom to pull the ball more. In general, an approach at the plate where strikes are actively hunted could lead to the barrel of the bat getting out in front quicker, and more solid contact to the pull-side.
Looking Ahead
Currently, Fangraphs’ Steamer projects Kieboom to slash .261/.335/.415 with a 94 wRC+ and 1.8 fWAR. This is nothing special, and, considering the production the Nats got from the position last year, would be somewhat of a disappointment.
However, these projections aren’t always accurate. Below are two possible ways Carter Kieboom’s 2020 could go, one for each extreme:
- Best Case Scenario:
- He follows in Turner’s footsteps and becomes more aggressive at the plate at the major league level. His K% and BB% revert back to around where they were in AAA.
- He continues to hit the ball hard at a consistent rate.
- His defensive transition from shortstop to third base goes well, results in positive metrics.
- 3.0 – 4.0 fWAR
- Worst Case Scenario
- He continues to be tentative at the dish, and his K% stays high.
- The hard contact he was making in 2019 turns out to not be repeatable.
- He struggles to transition to third base, results in negative metrics.
- 0.0 – 1.0 fWAR
Should Kieboom be expected to completely replace Rendon’s production in 2020? No, but to be fair, there are very few third basemen in baseball who could accomplish that. However, could a lineup including Kieboom, along with players like Victor Robles and Trea Turner showing improvement and staying healthy, end up being better than the World Series winning lineup of 2019? Absolutely.
So, maybe Carter Kieboom’s first taste of Major League Baseball didn’t go the way anybody wanted it to. The point is, he’s young, full of potential, and still getting better. To quote one of Davey’s many mantras from the 2019 season, ‘Often bumpy roads lead to beautiful places’.
All data courtesy of fangraphs.com, unless otherwise specified. All GIFs created on giphy.com.
