After the Red Sox signed Masataka Yoshida to a five-year, $90 million contract this offseason -- representing the largest contract ever awarded to a position player coming from Japan to MLB -- opinion about the transaction outside of Boston was mixed at best. After all, Yoshida was small (5-foot-8, 176 pounds via Baseball Reference). He was old for rookie standards, turning 30 this coming July. And more than anything, he was unproven, having excelled in Japan’s Nippon Professional Baseball (NPB) for years but never having seen the world’s best competition.

Shortly into his debut season in Boston, it appeared that the naysayers couldn’t have been more correct. Through April 19, Yoshida had played 13 career games, securing a paltry .167/.310/.250 batting line with one home run, adding up to a .560 OPS.

But since April 20, Yoshida has turned a corner. He has a hit in all 16 games he has played since then, and his 28 hits and 48 total bases over that span are both most in MLB. He has a remarkably efficient .438/.479/.750 line with five homers since April 20 (1.229 OPS), leading all players with at least 40 plate appearances in both batting average and OPS. His turnaround is a major reason why Boston ranks third in MLB with 5.8 runs per game for the season, and why he was named AL Player of the Week for May 1-7.

So what has changed for Yoshida? Is his 16-game (and counting) hit streak merely noise from a small sample size? Or are there sincere signs that his breakout, which has helped the 21-15 Red Sox hang around in a historically competitive AL East after largely being predicted to finish last for a second consecutive season, is one to stay? We dive into Yoshida’s approach and his advanced stats to gauge if Boston’s $90 million man is the real deal.

Does Yoshida have the power?

To begin the tale of Yoshida’s turnaround, we can travel way back to December 2022, when he was first signed by Boston. What did scouts and executives have to say about him at the time, and which of their words have been proven right?

We’ll start with those who were anti-Yoshida. Anonymous MLB executives were pretty unanimous in what their perceived flaws of Yoshida’s game were: lack of power and limited defensive ability. For the most part, the latter trait has been proven correct this season. Yoshida ranks in the 12th percentile of Baseball Savant’s “Outs Above Average” metric (though to be fair, the rookie left fielder plays next to a wall that’s a bit tough to get used to). But the prior trait has fluctuated over the course of the year.

After a World Baseball Classic in which Yoshida hit two homers and 13 RBIs in seven games -- the latter of which set a WBC single-tournament record -- Yoshida’s stock couldn’t have been higher. Yoshida notably had a game-tying three-run home run in the semifinals against Mexico, a game that is ranked as the best in WBC history by MLB.com, and he and Shohei Ohtani were the only All-Tournament team selections from the champion Japanese squad.

But early in his MLB career, that power was not there at all. His plate discipline was pristine, as he only struck out on 8.6% of his plate appearances through April 19. But when he did make contact, he could not keep the ball off the ground. He had a mere .275 expected slugging percentage over that span, via Statcast, and his average launch angle of -5.1 degrees was second-lowest among 276 players with 25-plus batted balls in that span, ahead of only Jean Segura (-6.0).

Since April 20, though, Yoshida has emphatically flipped that trend. His average launch angle over that span is 5.9 degrees, significantly higher despite still being below the MLB average of 12.1. As a result, he’s been able to consistently hit balls out of the infield, with an xSLG of .730 that has nearly tripled where he was through his first 13 games.

To phrase this even more simply: When you get the barrel on the ball, good things happen. And Yoshida has done this drastically more often since April 20, suggesting there’s much more to his 16-game hit streak than luck. Through April 19, Yoshida only had one barrel in 58 plate appearances (a rate of 1.7%). Since then, his barrels/PA rate is 12.7%, more than seven times higher than it was over those first 13 games.

Here is a breakdown of how several of Yoshida’s advanced hitting metrics have taken a remarkable turn since April 20 (see the MLB glossary for detailed clarifications of any terms):

Yoshida’s advanced hitting metrics before vs. since April 20, 2023

• .182 expected batting average vs. .403 xBA
• .275 expected slugging percentage vs. .730 xSLG
• .271 weighted on-base average vs. .517 wOBA
• 85.1 mph average exit velocity vs. 93.0 mph
• 21.5% whiff rate vs. 10.5% whiff rate
• -5.1 degree average launch angle vs. 5.9 degrees
• 32.6% hard-hit rate vs. 59.3% hard-hit rate
• 1.7% barrels/PA vs. 12.7% barrels/PA

Yoshida leads MLB in the metric since 4/20 (min. 40 PA)

Yoshida may not ever be a 40-homer player, but he has shown sustainable signs of making hard and consistent contact over the past couple of weeks, a far cry from where he was to begin his career.

“It’s unbelievable what he’s doing right now,” Red Sox first baseman Triston Casas told MLB.com’s Ian Browne. “He got off to a slow start. I think everybody expected him to have his struggles early. But now, we see him hitting his stride and doing his thing. And, you know, when he's on, he can carry a lineup.”

What did Yoshida actually change?

It’s easy to quantify what is going better for Yoshida lately -- among the other metrics mentioned above, a lower whiff rate and a higher launch angle have paid dividends. But why have the rookie’s advanced metrics begun to ramp up in such a way? The answer is in his approach.

Entering a three-game series in Milwaukee from April 21-23, Yoshida, following some consultation with the coaching staff, opened up his batting stance. A slight adjustment led to him seeing the ball far better than he was earlier in the season. Hence the numbers you saw above: Yoshida is not only making contact more often, but also making harder contact when getting the bat on the ball.

Since that trip to Milwaukee, Yoshida has had at least one hit in every game.

“I can pick out the balls that I should swing at, so I think that’s why I’m doing well,” Yoshida told Browne. “I'm focused on my batting form, especially my stance. So, stance-wise, I'm stepping with my right foot back a little bit. Then, it makes me more comfortable to see the ball. I haven’t changed anything swing-wise.”

Indeed, it was changing the stance, not the swing, that has led to Yoshida’s outburst so far. After all, the swing was successful enough to set the WBC record in RBIs. But Yoshida’s stance adjustment came from the “hitting group,” as manager Alex Cora calls it, led by assistant hitting coach Luis Ortiz.

“With Luis especially, they talked about it, they made some adjustments,” Cora said. “You can see the hands, where they’re at right now, a little bit more relaxed. We’re learning who he is.”

High-end plate discipline

What did the scouts who were in favor of the Yoshida signing have to say? The biggest points of emphasis were plate discipline and the ability to get on base -- points that were backed up by his stellar 80/41 K/BB ratio and .447 on-base percentage in his final NPB season.

“For us, the thing that really stood out from all angles from a scouting angle, from breaking down the performance, is just the quality of the at-bat,” Red Sox chief baseball officer Chaim Bloom said shortly after the signing. “There’s a very unique combination of contact skills and strike-zone discipline and the ability to impact the baseball that we feel has a chance to really impact the game at the Major League level.”

“I say he’s like the Japanese Juan Soto,” former MLB outfielder Adam Jones, briefly a teammate of Yoshida's in Japan, told The Athletic in November. “He can hit the ball to all fields, all speeds. Like Soto, he hits everything — and walks, and doesn’t swing outside of the zone.”

While Yoshida’s ability to hit for power has improved over the course of his hit streak, his elite plate discipline has been on display since Day 1. Yoshida has only struck out on 8.5% of his plate appearances, the fourth-lowest rate among 188 players with 100-plus plate appearances. This is largely due to his selective approach at the plate, as he has only chased on 21.8% of pitches outside the strike zone -- ranking in the 83rd percentile, well below the MLB average of 28.4%.

And even when he has chased, good things have happened. Yoshida has made contact on 79.2% of his swings to come on pitches outside of the zone, ranking fourth among 215 players with at least 50 such swings. When expanding to all pitches, Yoshida’s ability to make contact still stands out. His whiff rate of 16.0% ranks in the 91st percentile, much better than the MLB average of 24.7%.

Handling the heat

But as it pertained to Yoshida’s ability to make the jump from Japan -- where he batted .327/.421/.539 with 133 homers and 467 RBIs across seven seasons -- to the U.S., there was one specific characteristic that Boston loved about him. 

“What we really watched very clearly when we saw him face the relievers in Japan, they’re throwing 95, 96 [mph]. And there are only a few arms that can do it [in Japan], and he handled those pitchers with great acumen,” Yoshida’s agent, Scott Boras, said in December. “[He] showed power and had the same level of strike-zone control with velocity that he had for the other pitchers, so those are things that are very impressive about him.”

“I think the most impactful thing,” Red Sox hitting coach Pete Fatse added, “is the ability to hit velocity.”

The pitchers throw harder in MLB than anywhere else, but the Red Sox brass nailed that Yoshida would be well-equipped to handle this. In plate appearances ending on pitches of at least 95 mph, Yoshida currently has a .435 batting average, .739 slugging percentage, and a .525 wOBA -- all of which rank in the top 10 among 96 players with at least 20 such PA this season.

Yoshida’s improvement vs. movement

As for the pitches that don’t go so fast? Therein lies arguably the biggest difference in Yoshida’s production since the beginning of the season.

Even when Yoshida was generally struggling early on, his performance against 4-seam fastballs was strong. Before April 20, Yoshida had a .350 average, .458 OBP and .500 slugging percentage on 24 plate appearances ending in 4-seamers.

But where the turnaround has been most pronounced is in Yoshida’s performance against breaking and offspeed pitches, which are defined by Baseball Savant as pitches including sliders, curveballs, changeups, splitters and sweepers. Yoshida had major problems against such throws early in the season, only having one hit in 19 at-bats ending on such pitches.

Since then, Yoshida has dominated such pitches, to the likes of a .409/.462/.818 batting line on 26 plate appearances. 

Yoshida against breaking/offspeed pitches before vs. since April 20, 2023

• .053 batting average vs. .409 batting average
• .172 expected batting average vs. .404 xBA
• .143 OBP vs. .462 OBP
• .105 slugging percentage vs. .818 slugging percentage
• .229 expected slugging percentage vs. .857 xSLG
• .127 weighted on-base average vs. .521 wOBA
• .222 expected wOBA vs. .532 xwOBA
• -5.1 degree average launch angle vs. 11.1 degrees

These differences are stark, giving a clear look into exactly how Yoshida’s hitting streak has come around. Yoshida could always hit velocity, as Boston felt strongly about all along. But if his improvements against the filthier stuff are here to stay, Yoshida just might prove himself to be worth every single penny that Boston spent on him -- all nine billion of them.