Darin Ruf, the Best Hitter on a Playoff Team

I’ve always been a huge Darin Ruf fan, so getting to write about his 2021 success is a little bit more meaningful to me than it would be for almost any other player. Ruf is the last player I remember my grandfather singling out before he passed away, with the thought that Ruf, then a young prospect in the Phillies system, had the potential to be a productive big leaguer for our favorite team.

That was nine years ago. The Phillies promoted Ruf in late 2012 for his first cup of major league coffee, but he never amassed more than 297 plate appearances in any season for them. The bat was decent — Ruf posted a 105 wRC+ over 833 plate appearances, including a 125 wRC+ during his 2013 rookie season — but poor defensive numbers kept him barely above replacement-level in almost 300 games with Philadelphia. He was traded to the Dodgers in November of 2016, and even before he had an opportunity to make his organizational debut, Ruf’s contract was purchased by the Samsung Lions of the KBO. For three years, he raked in Asia, earning himself a minor league deal with the Giants for the pandemic-shortened 2020 season. (I was pretty excited.) A year later, he’s now the best hitter on a playoff-bound team (Kris Bryant is a notable omission from this list — he has a 119 wRC+ in 128 plate appearances with the Giants so far):

It’s no secret that the Giants have been receiving incredible production across their entire lineup. Their position players have posted a collective 113 wRC+ this season, a figure that ranks second in the majors among teams’ non-pitchers. But even in a lineup filled with players having above-average offensive seasons, Ruf stands out with his .279/.401/.544 slashline and 155 wRC+. That wRC+ ranks seventh in the majors among players with at least 250 plate appearances overall, sandwiched between Juan Soto (156) and Shohei Ohtani (154). That’s pretty phenomenal company, and it inspires two obvious questions. First, how did Ruf become one of the best hitters in baseball, at least this season? And, of course, how sustainable is this?

The answer to question No. 1 requires a short primer on what makes Ruf tick. Given the theme of some of the articles I have written recently, in which I have discussed how the league-average hitter produces negative value by run expectancy when swinging, there’s a certain amount of poetic justice for this baseball writer that Ruf almost never swings. Indeed, Ruf only takes a hack at 37% of pitches, the third-lowest rate in the majors among players with at least 250 plate appearances. The group of hitters who swing this infrequently is an interesting one, to say the least:

Yes, at least in terms of swing rate, Ruf finds himself right there among Yasmani Grandal, Max Muncy, and Soto three hitters who are having some of the finest offensive seasons in all of baseball. Once again, that’s pretty good company. In fact, as you can see, most of the hitters on this list are having solid seasons, though not all of them — the exceptions being Brett Gardner and Josh VanMeter — are above a 100 wRC+.

What’s also interesting here, though, is that Ruf’s discipline looks like it may lag behind the rest. At 36.3%, he has the worst zone-swing differential (what I’m calling Z-Swing% minus O-Swing%) here, which may hint that while Ruf chooses not to swing most of the time, his eye at the plate still isn’t that sterling. This is particularly interesting when we consider that his 2021 zone-swing differential isn’t that much lower than his career 37% mark coming into this year, implying that, at least in this area, there’s no real improvement from the player he’s always been. He also doesn’t compare all that well with the rest of the league. This season, Ruf ranks 165th in zone-swing differential out of a total of 270 hitters with at least 250 plate appearances.

The rate itself is a little dependent on two important factors — namely, Zone% itself and the fact that, the higher your Z-Swing%, the less likely it is for your Swing% to be among the 10 lowest in baseball — but it’s worth noting that Soto ranks 17th in zone-swing differential and still appears on this list. As far as Ruf is concerned, he sees very little in the strike zone: His 39.4% zone rate is 27th-lowest among that group of 270 hitters, and yet he still swings at nearly one-in-four pitches not in the strike zone. His discipline numbers would probably be even better if he cleaned up that differential a bit.

But zone-swing differential aside, the fact that Ruf doesn’t swing often is really fascinating, especially in the context of his low zone rate. This tendency gets him into more favorable counts more often, with more than 31% of the pitches he’s seen this season coming while ahead in the count, a 91st percentile mark. That’s by far the highest rate of his career. The two other seasons Ruf saw more than 1,000 pitches, 2013 and ’15, just 26.6% and 25.8% of his pitches seen, respectively, came while ahead. Even last year, in his return to the majors, he was ahead in the count for only 28.6% of pitches seen, a 58th percentile mark.

There are certainly more words to be written about how luck and handedness splits have played into Ruf’s performance, but his decision to swing at one of the lowest rates in baseball feels most notable. It may explain why his top line results have been so good, but perhaps not entirely, as Ruf has the second-highest xwOBA in baseball (out of 258 with 300 results) on plate appearances ending when he’s behind in the count as opposed to “merely” the 20th-best xwOBA while ahead (out of 240). Relative to himself, he’s still better while ahead (.501 xwOBA ahead versus .338 xwOBA behind), of course, but his ability to still be solid when behind makes him a really tough hitter to face on the whole.

And that brings us to the second question: Ruf’s sustainability. He hits the cover off the baseball, posting elite barrel rates and expected statistics. Ruf also notably stands out in a statistic that has been referred to as “joint rate,” which captures batted balls that are both hard-hit (95+ mph EV) and are hit in the sweet spot (8-32 degree LA). These batted balls are kind of like barrels, but they don’t have as high of a bar to clear: barrels make up around 8% of events this year, while balls in this hard-sweet category make up more than double that (17.8%). The downside, though, is that you lose some wOBA: barrels have produced a 1.348 wOBA this year, while hard-sweet events have produced “just” a .920 wOBA in comparison. Effectively, you’re sacrificing about 30% of wOBA for an event that happens more than twice as often. As a result, it still seems like a pretty solid way to evaluate a hitter, even if it’s not quite as good as barrels. Just take a look at the leaders:

Now it is worth mentioning that, based on a quick look, I found that these types of events are not as sticky year-over-year as barrels, nor are they as well correlated as with wOBA or xwOBA on contact. This demonstrates that barrel rate is still a better measure of hitter skill than joint rate, hinting that while Ruf’s production is certainly fantastic, he is probably still outperforming his true-talent level. And that’s OK — I wasn’t expecting to come out of this research with the conclusion that Ruf’s performance is 100% sustainable going forward. Plus, age will also certainly be a factor in future seasons; Ruf turned 35 in July.

But what’s truly great about Ruf is that his performance is mostly sustainable, which is about as good of a conclusion as one could ask for. While the discipline is likely more a result of him choosing not to swing most of the time than him being able to better discern between in- and out-of-zone pitches, and the pop is likely the result of some extra luck rather than true barrel-based skill, there’s a lot here to suggest that what Darin Ruf is doing is mostly legitimate. He won’t be a 155 wRC+ bat in the future, but with some projection systems having him as high as in the low-120s, there is a lot to make us think that Ruf has truly become a well above-average big league hitter. He’s been quite the find for the NL West-leading Giants, and brings me plenty of joy knowing that my grandfather might have ended up being right.