May has been an eventful month for Lourdes Gurriel Jr. for two reasons.

First, because on May 8, he obtained his United States citizenship in a moment that he deemed “one of the most important days of my life.” He was even able to celebrate with his brother, Yuli Gurriel, who happened to be in Arizona immediately afterward as the D-backs opened a three-game series with the Miami Marlins.

The other reason is that Lourdes might be the hottest hitter in baseball over the past two weeks. In what is arguably the best month of his major league career so far, he is slashing an eye-popping .391/.500/.891 in 56 plate appearances.

It should also be noted that my cohost on the PHNX D-backs Podcast, Derek Montilla, dyed his hair purple this month in honor of Lourdes. Derek dyed his hair on May 2, in fact, which is the day before Gurriel’s season turned around dramatically. Coincidence? I think not.

Although Gurriel is arguably the current frontrunner for N.L. Player of the Month, it’s probably too early to call this a breakout for the 29-year-old outfielder. Heck, Gurriel had a season slash line of .265/.303/.382 little more than two weeks ago. Numbers shift quickly at this stage of the season, and Gurriel is notoriously streaky.

Nonetheless, there are good reasons to believe that what he has accomplished in 2023 — or, better stated, in May — could have real staying power. Let’s dive in.

Lourdes Gurriel showcasing career-best plate discipline

It is one thing for a hitter to go on a tear by swinging at a whole bunch of bad pitches and finding ways to do damage anyway. That is the type of two-week hot streak that lasts for, well, two weeks.

What Gurriel has done so far in May is different. Not only is he doing far more damage on the pitches he is hitting — more on that later — but he has gotten far more selective with the pitches he is swinging at in the first place. Obviously, these things go hand in hand.

Entering play on Friday, Gurriel’s swing percentage this season sits at a career-low 45.8 percent. It is no coincidence that the number has dropped considerably in the past two weeks as Gurriel has found his stride offensively. As of now, this is the first season of Gurriel’s career in which he has swung less frequently than a league average hitter.

Granted, taking more pitches is not necessarily good. It depends on where those pitches are located.

Gurriel, though, has seemingly made all the right decisions in recent days. While his swing rate on pitches in the strike zone has held relatively steady, his swing rate at pitches outside the zone (also known as chase rate or, more technically, O-Swing%) has plummeted. It comes as no shock that Gurriel’s chase rate began its precipitous drop about two weeks ago, when his offensive breakout began.

After seven weeks of the season, Gurriel’s chase rate sits at 28.1 percent, which is slightly below the league average of 28.3 percent. Historically, it has generally been above the league average, topping out at 36.2 percent in 2019.

Over the past 15 games, Gurriel’s chase rate is just 19.7 percent. For reference, a 19.7 percent mark last season would have been the seventh-lowest mark in baseball among qualified hitters.

With the exception of a brief stint in the middle of the 2021 season, Gurriel’s chase rate has never been this low over a 15-game span in his entire career.

Only time will tell whether a chase rate under 20 percent is sustainable for Gurriel in the long term. It probably isn’t. Nonetheless, spitting on pitches outside the strike zone was a strength for Gurriel last year too, and he is clearly a much more selective hitter now than when he first came into the big leagues.

As would be expected, Gurriel’s reduced chase rate has directly impacted his strikeout rate. He has struck out just 14.9 percent of time this year, which is the lowest mark of his career. Meanwhile, Gurriel is also walking a career-high 8.1 percent of the time. It is amazing how big of a difference improved plate discipline can make.

Lourdes Gurriel’s power appears to be back

When the Diamondbacks acquired Gurriel last December, they did not necessarily need him to hit for power. He was a much-needed right-handed hitter, and a good one at that. He hit .291 for the Blue Jays last year. That easily would have topped all other D-backs hitters in 2022.

Nonetheless, after averaging 29 dingers per 162 games played in his first four seasons, Gurriel only hit five homers in 2022. There was an undeniable sense of mystery in the baseball community as to why Gurriel’s power suddenly disappeared, and whether it could be reasonably expected to return in the future.

Some, including D-backs general manger Mike Hazen, suspected that a midseason hamate (wrist) injury might have played a role.

“There was a little bit of a power dive a little bit last year,” Hazen said after the trade. “We feel like the hamate could have had something to do with that. That has now been fixed. We’re excited to add this guy into our lineup. We think he has a chance to be one of our better hitters.”

Fast-forward to now, and Gurriel has been everything the D-backs could have hoped for and more. Not only has he been arguably their best hitter, but he has also hit more home runs in the first half of May than he did all of last season.

So, on to the inevitable question: Is this sustainable? Can Gurriel really hit 26 homers this year, as he is currently on pace to do?

There are a few ways we can tackle this. The first is to simply look back at the seven dingers he has hit to date and evaluate their relative flukiness. Gurriel isn’t the type to hit tap measure homers — his longest dinger of the year is a meager 413 feet — but Statcast data suggests that, if anything, Gurriel actually deserves one more homer than he currently has.

Another way we can look at this is to take a closer look at Gurriel’s batted ball profile to see if anything has changed dramatically. Despite what one might expect, Gurriel is not hitting significantly more fly balls this season than he did last year. In fact, his ground-ball, fly-ball and line-drive rates are all very similar to their 2022 marks. Moreover, Gurriel’s results on grounders and liners have held relatively steady from last year.

What has changed dramatically is Gurriel’s ability to do damage on fly balls. Last year, he hit just .125 with a .350 slugging percentage on fly balls compared to .444 with a 1.296 slugging percentage so far this year. The expected stats provide helpful context:

Based on expected batting average (xBA) and expected slugging percentage (xSLG), suffice it to say that Gurriel’s results on fly balls last year were probably a bit unlucky and he’s arguably had more than his fair share of good luck so far this year. Either way, the reality is that fly balls were something of a waste of time for Gurriel in 2022. He was better off hitting grounders and line drives. This year, fly balls have been his greatest weapon.

As far as long-term sustainability is concerned, barrel rate is another helpful stat that warrants a look. A “barrel” is defined as any batted ball that has historically produced a batting average of .500 or higher and an expected slugging percentage of 1.500 or higher. Essentially, these are the very best batted balls — the kind that often go for dingers and extra-base hits — and they are also very often fly balls.

Last year, Gurriel had a barrel rate of just 3.8 percent. That means that 3.8 percent of Gurriel’s batted balls were barrels, which is relatively low compared to the league average of 6.8 percent and extremely low compared to Gurriel’s career barrel rate of 8.3 percent. This year, Gurriel is running a barrel rate of 9.0 percent.

It’s too early in the season to put all that much stock in that number, but it is an important figure to monitor as the season goes on. Baseball statisticians have found that barrel rate is actually more predictive of future home run rate than current home run rate is. If Gurriel’s barrel rate hangs in the nine percent range for a while, it’s a good sign that his power is, in fact, back.

Even if Gurriel’s power slips a bit over the course of the season — an outcome that seems likely given Gurriel’s up-and-down past — he has already provided so much value in the first month and a half of the season that fans probably should not be too disappointed by it.

The reality is that it is May 19, Gurriel is slashing .310/.373/.552 and the D-backs are 25-19. At this point in the season, it is hard to imagine how things could have gone much better for Gurriel and the D-backs.

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Top photo: Stan Szeto/USA TODAY Sports