Marcus Stroman is one of the very best pitchers in baseball. Since the beginning of last season, his 6.7 WAR is 13th in the league, right behind Jon Lester, Stephen Strasburg, and Jose Quintana — and just ahead of Jacob deGrom, Madison Bumgarner, and Zack Greinke. If you’re a believer in ERA, you probably didn’t think much of his 4.37 mark last year but are much more impressed by this season’s 2.99 figure. His FIP has remained steady, right around 3.70.

Despite a listed height of 5-foot-8, Stroman has recorded one of the league’s higher average fastball velocities. While there’s typically a relationship between velocity and strikeouts, that’s never been integral to Stroman’s success. His game is about inducing ground balls. It works well for him, but it does also leave room for some to regard him as something less than an ace.

As far as the ground-balling goes, Stroman’s elite. His 60.1% ground-ball rate topped all pitchers last season. He’s actually improved upon that figure this year, recording a 62.6% rate so far. The right-hander’s 61.2% ground-ball rate in 2016 and 2017 is the second-highest over a two-year period (min. 300 innings pitched) this decade behind Dallas Keuchel’s 62.6% mark in 2014 and 2015. Tim Hudson is the only other pitcher to exceed 60% grounders over a two-year period since 2010.

Inducing a lot of ground balls is a good thing, largely because ground balls can’t become homers. Stroman’s 0.87 HR/9 over the last two years is indicative of that; it places second among qualified starters only to Michael Fulmer’s 0.80 mark. Even after dropping the inning requirement to 250, Stroman sits behind only Fulmer, Clayton Kershaw and Kyle Hendricks. Stroman’s ability to limit homers helps make him one of the league’s better pitchers, even without an abundance of swings and misses.

Digging a bit deeper, though, we do see some causes for concern is Stroman’s profile. His home-run rate on fly balls (HR/FB_ rate is right around 16%, in the bottom quarter of starting pitchers over the last two seasons. While that is a problem for Stroman, it isn’t one that’s unique to ground-ball pitchers like Stroman. Of the 60 qualified starting pitchers over the last five single seasons with at least a 52% ground-ball rate, the collective HR/FB rate is 11.7%, compared to 10.7% for the rest of starters.

This can help make it seem as though these ground-ball pitchers are getting hit particularly hard. Whatever they allow in additional home runs per fly, though, doesn’t compensate for the ability to limit flies in the first place. Ground-ball pitchers mitigate damage on fly balls by allowing fewer of them in the first place. There’s an inverse relationship between ground-ball percentage and HR/9, as the graph below shows.

That relationship gets even stronger when you look over the course of several years, as home-run rates can have some variance year-to-year. So we know that Stroman’s ground-ball rates are a good thing because they allow him to limit homers, but that isn’t exactly proof that he isn’t getting hard. Stroman’s career BABIP against is .305 and over the last two seasons it has been .310. When batters put the ball in play against Stroman, in other words, they’ve been more likely to get a hit than against other pitchers.

We can separate those numbers by batted-ball types and compare them to league average.

Marcus Stroman Career BABIP on Batted Balls BIP Type Stroman MLB Difference GB .226 .239 -.013 FB .154 .128 .026 LD .714 .681 .033

Overall, Stroman has conceded a BABIP about 10 points higher than league average — a point that lends credence to the theory that he gives up a lot of hard contact. Exit velocity is no help either. Out of 171 pitchers who’ve at least 1,000 pitchers this year, Stroman’s average exit velocity of 88.2 mph ranks 142nd. This isn’t a new development, either: the 89.9 mph average exit velocity he allowed last season was 118th out of 119 among pitchers with at least 2,000 pitches.

Just as we did above, we can break these exit-velocity numbers down by BIP type, as well. Here are Stroman’s exit-velocity numbers from this season by batted-ball types and where he ranks among pitchers with at least 1000 pitches, per Baseball Savant.

Marcus Stroman Exit Velocity on Batted Balls BIP Type Exit Velocity Rank (Out of 171) GB 86.5 mph 170 FB 92.5 mph 139 LD 92.9 mph 67 SOURCE: Baseball Savant Ranks among pitcher with 1,000 pitches in 2017, with lower exit velocity being better.

We probably don’t have to worry about the line drives, on which batted-ball type Stroman ranks in the middle of the pack there. By fly balls, however, he sits in the bottom fifth, which isn’t great. And where he’s getting hit hardest is on ground balls, a fact which drives his exit velocity numbers up relative to other pitchers as he gives up a ton of ground balls.

Stroman gets those ground balls on his sinker, a pitch he throws 58% of the time, third in baseball among qualified pitchers behind only Jake Arrieta and Chad Kuhl. Here’s where the ball tends to go against his sinker, per Baseball Savant.

That’s a lot of balls in the infield, and most of those balls in the outfield are singles. His defense certainly helps, but there’s a reason Stroman leads the majors with 27 double plays this season and why his mark of 49 double plays over the last two seasons is third only to Martin Perez and Carlos Martinez.

On the flip side of the coin, when those balls get in the air, they hurt Stroman more than the average pitcher. Here’s Stroman’s wOBA against during his career on different batted-ball types compared to league average.

Marcus Stroman Career wOBA on Batted Balls BIP Type Stroman MLB Difference GB .204 .218 -.014 FB .412 .366 .046 LD .703 .677 .026

We keep going back and forth on how he gets hit hard and why it does or does not matter, but that’s a pretty significant difference in fly balls compared to his peers. A look at his batted-ball profile reveals how Stroman minimizes those damaging plays.

Marcus Stroman Career Batted Ball Profile BIP Type Stroman MLB GB 59.5% 44.8% FB 21.9% 34.5% LD 18.6% 20.7%

Compared to the average pitcher, Stroman is trading 15% of his fly balls for ground balls. Below is an illustration of how that can play out. I’ve set up a square with four quadrants below. Each one has wOBA against based on a profile combining league-average batted balls and wOBA against batted balls with Marcus Stroman’s average batted balls and wOBA against batted balls.

Marcus Stroman as an Average Pitcher MLB wOBA on GB/FB/LD Stroman wOBA on GB/FB/LD MLB GB/FB/LD % .364 .379 Stroman GB/FB/LD % .336 .342

A completely average pitcher both by batted-ball type and result is going to give up a .364 wOBA on those batted balls. If that same pitcher just switched to Stroman’s ground-ball and fly-ball rate, that wOBA against would drop nearly 30 points. As we can see, Stroman gets hit a bit harder than the average pitcher, especially when it comes to fly balls. If Stroman took the same results except also dropped to a 45% ground-ball rate, his wOBA on batted balls would be .379, about 15 points above average. Because Stroman can induce so many ground balls, his wOBA against ends up well below average (in a good way). Those figures aren’t going to show up in HR/FB or BABIP or average exit velocity, but it helps explain why Stroman is such a good pitcher. As long as he keeps the ball on the ground and limits walks to a reasonable level, he doesn’t need to worry about his lack of strikeouts.

Stroman might not stay completely the same. Perhaps he’ll trade some ground balls for strikeouts in the future. Maybe he’ll string together some Cy Young-level seasons like the pitcher below, with an admittedly significant age caveat limiting their comparability.

First Four Years in the Majors Name Years Age IP K% BB% HR/9 BABIP GB% HR/FB ERA (ERA-) FIP (FIP-) Felix Hernandez 2005-2008 19-22 666.1 21.1 7.7 .88 .312 58.0 13.3 3.80 (88) 3.70 (85) Marcus Stroman 2014-2017 23-26 521 19.8 6.4 .76 .305 59.5 12.9 3.63 (86) 3.48 (82)

Hernandez finished second in the Cy Young the following year before winning it 2010. That’s something to dream on.