Investigating the improvement of the Royals offense

On May 16th, the Kansas City Royals offense was in dire straits. With just over a month of games played, the team had collectively hit a 77 wRC+, which was 27th in baseball. Their 118 runs scored was also 27th. Despite coming off an offensive outburst in Colorado, in which the Royals scored 26 runs in a three-game set, the brass decided it was time to make a change. The Royals fired hitting coach Terry Bradshaw, replacing him with Alec Zumwalt, who had been serving as Senior Director for Player Development and Hitting Performance.

Since this change was made, the offense has improved considerably. The team wRC+ since May 15th is 103, good for 14th in baseball, while their 324 runs scored is 21st. It’s still far from an elite unit, but it’s much closer to middle of the pack than bottom of the barrel now. Their season-long wRC+ now stands at 96, which would be their best season by wRC+ since 2015, and the fourth highest of the Dayton Moore era.

So what specifically has led to this turnaround? Can we credit this to the change at hitting coach, or are other factors more of a reason? Let’s dive in.

Note: All stats cited are through games played August 10th.

Hitting performance under Bradshaw vs. under Zumwalt

We will begin by looking at players who have received regular playing time under both Bradshaw and Zumwalt. Most such players are veterans, so you can debate how much influence the hitting coach has on their performance, but let’s take a look anyway. There are eight players who received at least 50 plate appearances both before and since May 16th:

Most of these guys have been more productive since May 16th, with the only exceptions being Benintendi, who remained equally productive, and Dozier, who has been worse. While the strikeout and walk numbers haven’t changed much and in some cases have been worse, all six guys that have improved have hit for more power. So the improved production may be due to changes made by Zumwalt, or perhaps they are a result of...

Regression to the mean

It’s possible these players were simply underperforming and were due for some positive regression. It’s also possible that the pendulum has swung the other way and now they’re overperforming in some manner. Let’s take a look at some statistical indicators that could show this:

There’s a lot to unpack here. Merrifield had some poor BABIP luck early on, but his numbers ticked up as it regressed closer to his career average. Perez’s batted ball metrics have improved closer to what he did during last year’s home run binge. Witt has hit the ball harder and his BABIP and HR/FB% have ascended to levels that should be sustainable based on his profile. Lopez and Santana regressed closer to their career averages on batted balls and saw their numbers improve. Taylor is the case where his improvement seems clearly unsustainable: he’s seen a BABIP spike despite his batted ball metrics declining.

We should have expected some positive regression around that time of the year regardless, as offense tends to tick up as the weather warms and MLB quits monkeying around with the ball. Hence why I included league stats above: leaguewide BABIP and HR/FB% has increased in that time span. Another important factor to consider is...

Personnel changes

Thanks to a series of trades and subsequent call-ups, the lineup now looks much different than it did when Zumwalt took over. Since May 16th, the Royals have had five hitters make their major league debuts. They’ve also found more playing time since then for rookie MJ Melendez and almost-rookie Kyle Isbel. Let’s check out how these guys have fared under the tutelage of Zumwalt:

All the caveats of small sample size apply here, but to this point, these guys have mostly held their own at the major league level. This is vastly preferable to the replacement-level fodder that the Royals have so often run out there over the past five seasons. Having big bats in the lineup is important, but it’s also quite difficult to field even an average offense when guys like Ryan O’Hearn, Kelvin Gutierrez, and Cheslor Cuthbert are getting regular at-bats.

It’s inevitable that these rookies will take their lumps; the skill gap between AAA and the majors is not insignificant. Massey probably won’t BABIP .385 all year, and the group of players that can be productive with strikeout rates over 30% like Pratto is a short list. But the early results are encouraging and on the whole, these guys offer more ceiling than the typical AAAA waiver-wire guy.

Looking ahead

Based on player usage since the deadline, we can expect to see Melendez, Witt, Perez, Pasquantino, Dozier, Taylor, Pratto, and Lopez in the lineup daily, with Massey, Eaton, and Isbel also getting at least semi-regular playing time. The sample of games with this offensive unit is small, only nine games, but the early returns are excellent: 46 runs scored with a collective line of .266/.318/.448, good for a 114 wRC+. Some quick thoughts on each of these players going forward:

• MJ Melendez: He’s been on a heater in August even with a BABIP of just .208. He’s got a good chance of leading the team in wRC+.
• Bobby Witt Jr.: On one hand, he has only seven extra-base hits since the start of July. On the other, he has cut his strikeouts in that span after punching out in over 24% of his plate appearances in each of the first three months. Here’s hoping he can find a way to put together the power he showed in May and June with the bat-to-ball skills he’s shown lately.
• Salvador Perez: He’s absolutely crushed the ball since returning from the IL and based on last year, I have no reason to believe he won’t continue to do so.
• Vinnie Pasquantino: His results have finally started to catch up to his expected stats with a 152 wRC+ so far in August. I think he’ll finish the season strong.
• Hunter Dozier: He’s been scuffling since the All-Star break with a 42 wRC+ and just four extra-base hits. With a .208 BABIP in that span, he might be due for some positive regression, but it’s also possible he loses playing time to some of the rookies down the stretch.
• Michael A. Taylor: His numbers are buoyed by a hot May and June, but he hasn’t hit at all in August. I imagine he’ll see his BABIP regress and finish the season with a wRC+ below 100.
• Nick Pratto: He’ll need to follow the Matt Chapman blueprint for success, taking enough walks and hitting for enough power to offset the strikeouts and low batting average. I’m tempering my expectations.
• Nicky Lopez: His offensive success is almost entirely BABIP-dependent. If he can keep it over .300 as he has since the start of July, he can finish the season with a wRC+ in the 80-90 range.
• Michael Massey: He’s held his own in a small sample despite not hitting for the power he’s shown in the minors over the past couple seasons. As he receives more major league exposure, I think pitchers will increasingly exploit his aggressive approach at the plate.
• Nate Eaton: He’s done a bit of everything at the plate so far, but it’s important to bear in mind that his only extended stretch of minor league success prior to this year was a 66-game stint in rookie ball way back in 2018. I just hope he can be a useful utility guy.
• Kyle Isbel: He hasn’t been able to replicate his late-season success last year; a 51 to six strikeout-to-walk ratio just won’t cut it at this level. He’s really struggled catching up to high fastballs. Quick aside: for all the consternation about his ability to man center field, he’s graded out very well there by Outs Above Average.