Why this lefty is MLB's most under-the-radar ace

Hyun Jin Ryu starts against Stephen Strasburg and the Nationals on Sunday, and when he does, he'll have a Major League record of sorts to defend. Ryu has 45 strikeouts, and he's allowed just two walks. That's 22.5 whiffs for every walk, which would merely be the highest mark in a season of 40 innings pitched in the history of baseball.

That's not likely to last, of course, and it would be nothing more than an interesting early-season note, if not for the fact that last year, Ryu's 89 strikeouts and 15 walks gave him a 5.9 strikeout-to-walk ratio, the sixth best among pitchers with 80 innings. (Among those ahead of him: Justin Verlander, Chris Sale and Corey Kluber. Also, Robbie Erlin. Baseball is wonderfully weird.)

Ryu doesn't throw hard, as his 90.4 mph four-seam velocity is only in the 11th percentile. He doesn't have high spin, as his fastball spin rate is also in the 11th percentile and his curveball spin is about exactly average. In terms of "stuff," and likely also in terms of "notoriety," he's likely not even one of the top three lefties in his own rotation, what with Clayton Kershaw, Rich Hill and Julio Urias around.

What Ryu does have is a near-endless run of injuries and, perhaps, the unofficial title of "baseball's most under-appreciated starter." Ryu had a 1.97 ERA last year, and he has a 2.03 ERA this year. Combine those two years and compare it to the 147 pitchers with 125 innings pitched in 2018-19, and you get this wonderfully impressive list of Ryu and baseball's most elite aces.

1.99 -- Ryu, Dodgers

2.00 -- Jacob deGrom, Mets

2.19 -- Blake Snell, Rays

2.49 -- Trevor Bauer, Indians

2.52 -- Justin Verlander, Astros

2.63 -- Chris Sale, Red Sox

2.75 -- Aaron Nola, Phillies

2.77 -- Max Scherzer, Nationals

Name your advanced metric, and Ryu has been a Top 10 starter in it over the last two years. Here's wOBA, where he's between Verlander and Tyler Glasnow. Here's expected wOBA, where he's between 2018 All-Star Ross Stripling and Nola. Here's walk rate, where he's the best, and strikeout rate, where he's 17th, ahead of Nola and Kluber.

This isn't a fair fight, of course, because Ryu has thrown half as many innings as most of these guys. But how does a pitcher who doesn't throw hard and rarely stays healthy get to this point? It's worth finding out.

No discussion of Ryu can begin without a nod to his extensive injury history. After signing with the Dodgers in 2013, he made 56 starts with 344 innings in 2013-14, proving himself to be capably effective with a 3.17 ERA.

But even in 2014, the health issues began, as he missed much of May with left shoulder inflammation and part of August with a hip strain. Then, he basically disappeared for two straight years. Let's take a brief spin through his trips to the injured list:

2015: Zero innings pitched, left shoulder surgery.

2016: 4 2/3 innings pitched, left elbow surgery.

While he returned in 2017 -- he ended up going 973 days between wins -- it wasn't without further issue.

2017: 126 2/3 innings pitched, left hip contusion in May, left foot contusion in July.

2018: 82 1/3 innings pitched, left groin injury in June described as "torn off the bone."

Even in what's been a successful 2019, he hasn't been completely free of the injury bug.

2019: 44 1/3 innings pitched, missed one start with left groin strain.

The point here is one of expectations, really. Ryu will never be Scherzer or Verlander, who have made a point of throwing 200 innings on an annual basis, but he should never be expected to be that, either. The point is that when he's available to the Dodgers, he's generally been outstanding. Since the start of 2018, he's been more than that, which is more than a little impressive for a pitcher who seemed, for nearly two years, that he might never make it back at all.

Yet the reasons why he's been this successful are a little less clear. This isn't about spin or velocity, clearly, because he's not an overwhelming pitcher in that way. It's not even about an elite ability to avoid hard contact -- his hard-hit rate of 38.8 percent is slightly worse than the Major League average of 37.2 percent. His ground-ball rate of 50.9 percent is better than the 44.2 average, but it's also not in the top 20, either.

There isn't going to be that "one satisfying answer" to this, not in the way that you can point to Noah Syndergaard throwing flames or Kluber having a breaking ball that moves unlike anyone else's. Instead, let's give this a try with four reasons that all combine to be part of what makes Ryu so effective.

1) He has elite command, probably

We could probably stick with the "he's walked only two guys this year and his 3.5 percent walk rate since the start of 2018 is baseball's best for a starting pitcher" and get the point across, but there's also something else. Ryu throws five pitches at least 10 percent of the time, and at The Athletic on Friday, Eno Sarris identified a "command" metric that suggested Ryu is one of only six pitchers with at least five pitches that all have above-average command. Notably, Scherzer is on that list. More notably, so is Marco Gonzales, another successful lefty without elite velocity.

2) He gets to pitch with no one on base, a lot

"Don't walk people and you don't have to worry about runners on base" is somewhat obvious, but it's also not so clear just how big of an effect that can have.

Since the start of 2018, there have been 151 pitchers to throw 1,500 pitches as starters. Look at the top three, in terms of "most pitches thrown without runners on base."

69.5 percent -- Verlander, Astros

69.3 percent -- Ryu, Dodgers

67.5 percent -- Glasnow, Rays

It's a good list, with Snell, Zack Greinke and Luis Castillo also appearing in the top 10.

There's actually not as large of a difference here as you'd think for Ryu, because he's been good in all situations, which you generally have to be in order to get to that 1.99 ERA. But since the start of 2018, he's allowed a .596 OPS with the bases empty, and a .643 mark with runners on. It helps.

3) He's a lefty who can pitch to righties

Ryu is good against lefty batters, allowing a .282 wOBA to them since the start of 2018, which is the 19th best of 44 starters who have faced 100 lefty hitters. It's fine, it's good, it's solid.

But against righties? Ryu's .234 wOBA is the best of 54 lefties who have faced 200 righties in that time. It's just ahead of Patrick Corbin, Chris Sale, Snell and Kershaw. It's not in the same number of innings, obviously, but it speaks to what Ryu is doing here.

4) He's changing how his four-seamer and his fastball work off one another

If Ryu has one plus pitch, it's his changeup. Over the last two years, it's allowed the lowest average (.152) and the fourth-lowest slugging (.250) among changeups.

That was always his best pitch dating back to Korea, but the same couldn't be said for his four-seam fastball, which allowed a .276 average and a .405 slugging back in 2013-14, before his injury-induced hiatus.

Look what's happened to both of them as he's returned. The changeup has gotten lower. The fastball has been thrown higher, which fits in with the famously high-fastball happy Dodgers.

Back in 2013, there was a half-foot difference in height between the changeup and the four-seam. Now, it's a full foot, or double. Causation isn't correlation, but it's difficult to see this difference and not point out that his four-seamer over the last two years, which now comes in slightly slower than it used to, is allowing a .214 average and a .350 slugging, each better than they were when he arrived.

“It was good to watch Hyun-Jin do his thing,” said manager Dave Roberts, after Ryu needed just 93 pitches to shut out the Braves on Tuesday night. “Complete domination tonight. His feel, to strike the breaking ball, has always been elite. It’s hard to say he’s under the radar, but he’s an elite pitcher in baseball. It makes it fun to sit back and watch."

Ryu has been an elite pitcher in baseball, but it does seem to feel like he's under the radar. That's partially because of the other huge names on the Dodgers' roster and in his rotation, and partially because he's rarely been healthy long enough to to let his talent show. But whenever he's been out there, he's been effective. He's been more than effective, really. He's been elite.