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Seiya Suzuki has been hot in May — Is that sustainable?

Suzuki is making better swing decisions and getting better results

Chicago Cubs v San Diego Padres
Seiya Suzuki at the plate against the Padres over the weekend
Photo by Jayne Kamin-Oncea/Getty Images

The Cubs got off to a hot start offensively this season, however, over the last 30 days they’ve cooled off considerably. In March and April, they were among the hottest hitting teams in the National League by wRC+, wOBA, OPS, or whatever metric you wanted to evaluate. However, that was not true in May. In March and April the Cubs had a wRC+ of 118. wRC+ is a league and park adjusted metric that tells you how much better a team or hitter is at driving in runs than the average of 100, so the March/April Cubs were 18 percent better at driving in runs than the rest of the league. In May, the team’s wRC+ dropped down to 92, eight percent lower than the rest of the league.

That goes a long way to explaining why the team has struggled to get back to .500 over the last month. But it hasn’t all been struggles in May. At least one key player on the Cubs has been much better as the season went on, and if the Cubs are going to climb back into the playoff picture the Cubs are going to need Seiya Suzuki to continue along the path he’s been on in May. Today I want to take a look at what Seiya has been doing differently this month to see if it’s sustainable.

Seiya Suzuki started off slow this season, but over the last 30 days he’s been one of the top 20 hitters in the National League by wRC+, with a 146 during that time. May Suzuki has been 46 percent better than the league average hitter at driving in runs during that time period. Let’s take a look at his splits by month below:

Monthly splits for Seiya Suzuki

Mar/Apr 66 9.09% 24.24% 0.38 .254 .333 .373 .706 .119 .333 .315 97
May 108 14.81% 24.07% 0.62 .319 .417 .560 .977 .242 .393 .415 164
Select offensive stats FanGraphs

A couple of things jump out of this table right away: Seiya is walking a lot more in May than he did in March or April. Interestingly, he’s not striking out more or less, but he does seem to be generating better results on the balls he’s hitting. There are some elements of this that seem process driven to me, and some that seem to be more rooted in luck, so let’s take a look at both.

I expected to look at Seiya’s hard hit percentage and find that he’s hitting the ball harder in May than he was in March and April. He is not. Early in the season he had a hard hit rate of 48.8 percent, in May that is actually down to 37.9 percent. So I decided to look at a metric that could capture the quality of at bats Seiya is having and his process. I played around with the 15-game rolling graphs on FanGraphs with wOBA and was impressed with the inverse correlation between Suzuki’s wOBA and his z-Swing percentage:

Seiya’s wOBA and z-Swing%

First some definitions, wOBA is weighted on-base average, and it’s basically a fancy on-base percentage that gives you more credit for extra base hits than for singles and walks. z-Swing is a metric that tells us how frequently a hitter is swinging at pitches in the strike zone. Curiously, Seiya’s wOBA is inversely related to his in-zone swing decisions. In other words, he gets better results when he’s swinging at fewer pitches in the zone. That’s not to say he’s getting better results on pitches outside the zone (o-Swing) — his wOBA is inversely correlated to that as well:

Seiya’s wOBA and o-Swing%

To my eye, these results indicate Seiya’s results are more about selectivity. When he’s seeing the ball better, he’s making better swing decisions on pitches in the zone. He’s not just swinging at everything in the zone, he’s making decisions about which pitches to swing at and doing damage on those pitches. Interestingly, at least for now, that selectivity is translating into forcing pitchers to throw him pitches he can do the most damage on, as well. You can see that in both the pitches Suzuki is seeing this season and the results he has on them at Baseball Savant:

Suzuki pitch type by month 2023
Baseball Savant

You can look at his results on pitch type by month at Baseball Savant as well. I’ve simplified that table a bit so you can see Seiya’s results on fastball, breaking and offspeed pitches in April when he was struggling and in May when he was raking below:

Suzuki results by pitch type by month

Month Pitch Type Number Avg SLG wOBA Whiff %
Month Pitch Type Number Avg SLG wOBA Whiff %
May Fastballs 283 .286 .490 .386 19.8%
May Breaking 140 .361 .639 .445 24.1%
May Offspeed 46 .333 .667 .488 13.3%
April Fastballs 131 .300 .533 .410 18.9%
April Breaking 104 .250 .250 .244 20.5%
April Offspeed 36 .111 .111 .177 35.3%
Select stats Baseball Savant

It does appear that Suzuki has really dialed in his approach at the plate as the season has gone on. While his .393 BABIP in May suggests that some of this is luck on balls in play in addition to more selective swing decisions, one of the most impressive things I see in the data so far is that Suzuki in these numbers is that he’s making very good contact on every type of pitch right now. Being able to recognize the those pitches and wait on the ones he can do the most damage on suggests he’s creating some of that luck on his own. The Cubs will need him to continue to create that luck if they are going to get their offense back on track in June.