The Most Important Rookie Hitter in the Pennant Chase

Even before it began, the 2019 season seemed poised to become the year of the rookie hitter. That seems true every year nowadays, but it seemed especially so this year. Vladimir Guerrero Jr. and Fernando Tatis Jr. had a ton of anticipation surrounding their debuts, but there were other big names ready to introduce themselves as well. Eloy Jimenez was about to unleash his prodigious power upon the big leagues for the first time, Victor Robles was embarking on his first full season of showing off his game-changing speed in the majors, and Nick Senzel was going to finally try to put his injury problems behind him and show why he was the second overall draft choice in 2017. National prospect lists consistently laid out the excitement surrounding the next generation of great hitters, with our own Top 100 list featuring nine hitters in the top 10 prospects, and 17 in the top 20 (along with one two-way player).

Nearly two-thirds of the way through the season, many of those rookie hitters have shown the potential to carry the weight of a franchise on their shoulders. Unfortunately, most play for teams that won’t be challenging for postseason spots this season, so they will have to wait their turn to show off their talents in important fall baseball games. Others are playing on teams that will certainly be around in October, but they play at a spot that their organization was already doing quite well with. This piece isn’t about one of those guys, though. We’re here to talk about someone I think means more to his team’s postseason hopes than any other rookie in baseball.

This player might not be who you think it is. For starters, the subject of his piece isn’t one of the five guys I named in the opening paragraph. Those are the five hitters who were ranked in Eric and Kiley’s top 10 prospects and appeared in a major league game this season. They were all supposed to be pretty good, and for the most part, they have been. There is one guy, however, who has looked better than all of them.

Obviously, plate appearances are a caveat here, but 155 PAs is nothing to sneeze at. It’s about a quarter of a season — not enough to declare that this performance is 100% indicative of their true talent level, but long enough to take what they’re doing seriously. I picked these three offensive categories because I didn’t want to make this an enormous table that showed 15 different categories, and I wanted somewhat comprehensive and telling statistics that each told their own stories. wRC+ tells me what a hitter has done, xwOBA tells me what he should have done, and barrel percentage tells me how often he is centering up a baseball. There might be a better combination, but this one made the most sense to me.

Our mystery player barrels up the ball more than any of those top-10 prospects, has an xwOBA performance that far exceeds what any of the other players in this sample have done, and only Tatis Jr. is in his company in terms of wRC+. That seems like a pretty good start.

Alas, this is not an exhaustive list of every rookie hitter. Our mystery player is far from unique in being someone from outside the top-10 preseason prospects who has outhit his more-hyped peers. Some of the best hitters in baseball this season have been players who made their debuts and exploded out of the gates. Here, then, is our Mystery Player compared with some of this season’s other breakout rookies.

So he’s no longer the best on the list, but he still looks pretty good, right? He’s no Yordan Alvarez, and he isn’t the Statcast darling Peter Alonso is. But surprisingly, his wRC+ is actually a bit better than Alonso’s, while he’s barreling up the ball better than certified dinger god Daniel Vogelbach.

That’s nine well-regarded rookies that our mystery player has been compared to, and depending on how you weigh actual production vs. expected production, he’s been better than about seven of them. He’s third in the group in xwOBA and barrel percentage, and he’s tied for second in wRC+. That obviously doesn’t make him the best rookie hitter in baseball, but that’s not the point I wanted to make. My thesis was that he was the most important hitter to the playoff race, and here’s why.

Tatis Jr., Senzel, Alonso, and Reynolds all play for teams who sit at least five games out of the National League wild card race. That gap isn’t impossible to close, but it’s bigger than you’d want it to be in the fourth week of July, and there are a ton of teams ahead of all of them. The teams Jimenez, Guerrero Jr., and Vogelbach play for are all at least 11 games out of the American League wild card race. They were never in the hunt. The odds are very good that none of these seven players will be playing important games for their clubs past the second or third week of September. Some already aren’t.

That leaves Robles, Alvarez, and our mystery player. Robles plays an important role for Washington, who currently occupies the first wild card spot in the NL, but his offense hasn’t come close to that of the other two. Alvarez, meanwhile, plays for the positively loaded Houston Astros, whose offense has been worth an MLB-leading 95 runs above average this season. Alvarez, 22, is obviously a significant part of that, slashing .333/.406/.675 with 10 homers in just 29 games since being called up, but he’s also the team’s designated hitter. If you take out Alvarez’s production, Houston’s DHs have still hit .258/.344/.516 this season. When guys like Michael Brantley and George Springer are the ones taking your position’s PAs if you’re not around, it’s difficult to say you’re irreplaceable.

Keston Hiura is our mystery player, and he is irreplaceable. He’s played 37 games at second base for the Milwaukee Brewers, who are in control of the second wild card spot in the NL and sit just two games out of the division lead in the Central. In that time, he’s amassed a .331/.387/.613 batting line, homering nine times and stealing six bases in eight attempts. Like Alvarez, he’s had an incredibly impressive start to his career, but in Hiura’s case, he’s provided value for the Brewers where they didn’t otherwise have it.

Non-Hiura second basemen have hit .258/.329/.520 for the Brewers, but that’s a somewhat misleading line, as the vast majority of that production is credited to Mike Moustakas, who manned the position before Hiura was called up while Travis Shaw played third base. When Shaw was removed from the lineup, Moustakas moved to third base, and Hernan Perez took over second. Shaw and Perez are the ones Hiura is taking PAs from, and that’s where his value to the Brewers becomes clear. In 212 PAs, Shaw has been worth -0.9 WAR and just a 49 wRC+, while Perez has been worth -0.1 WAR and a 68 wRC+ in 160 PAs.

Hiura, 22, had plenty of prospect stock when he arrived in the big leagues, ranking 13th on Eric and Kiley’s preseason list. His promotion to the big league club didn’t include the fanfare that Tatis or Vladito’s did, but he was still seen as a top-rate talent before the season started. From his report:

“This is an incredible hitter. He has lightning-quick hands that square up premium velocity and possesses a rare blend of power and bat control. Hiura’s footwork in the box is a little noisier than it has to be, and if any of his swing’s elements are ill-timed, it can throw off the rest of his cut. This, combined with an aggressive style of hitting, could cause him to be streaky. But ultimately he’s an exceptional hitting talent and he’s going to play a premium defensive position. We think he’s an All-Star second baseman.”

There’s evidence that the timing concerns have shown themselves early in Hiura’s career, as he ranks in the bottom 15 in baseball in both contact rate and swinging strike rate. As far as his streakiness is concerned, he hasn’t gone through much of a cold streak yet, but he’s certainly on a hot one this month: A .397/.453/.750 line in 75 PAs during the month of July. He’s hit well against four-seamers (.397) and sliders (.461 xwOBA) both. He’s been exceptional, and he’s performed this well despite a walk rate of 5.8% that is lower than what he’s put up at any level of his pro career.

Watching Hiura swing a bat paints a good picture of the talent he has at the plate. A few days ago, Hiura stepped into the box to face Braves right-hander Bryse Wilson for the first time. The very first pitch he saw was a 96-mph fastball on the inner third, and Hiura swung late. Most of the time, that means a hitter got jammed, and the result is either going to be a broken-bat grounder to the opposite side, or a lazy fly ball. Hiura, however, hits it 404 feet.

The next clip features a slider from Kyle Crick. Crick throws a good slider — opposing hitters are 6-for-56 against it this season with a .170 xwOBA. He throws it where he wants to, with the pitch finishing about five inches off the plate outside. That wasn’t far enough away, however, to keep Hiura from hitting it out.

And just in case you’re afraid Hiura can’t pull a ball with authority, here he is turning a mistake from Tyler Mahle into a 440-foot bomb to left-center.

A Brewers lineup with Hiura at second base is more dangerous than any combination it could put together without him. His average speed and below-average glove prevent him from being the best overall rookie in the majors, and he doesn’t have the loud power tools of Alonso or Alvarez, but as a pure hitter, Hiura stands out. And if he keeps up his production throughout the playoff race, he’ll mean more to his team than any rookie in baseball.