Below-the-hood metrics suggest Orioles' Tomoyuki Sugano might be in trouble

35-year-old rookie Tomoyuki Sugano has been one of the most reliable Orioles' pitchers so far, pitching to a 3.54 ERA across five games. However, while his real ERA suggests a strong start, his expected ERA (xERA) tells a different story.

Sugano's 6.12 xERA is fourth worst in all of baseball and is 2.58 runs worse than his real ERA. For reference, Astros' Ronel Blanco had the largest gap between ERA and xERA in 2024, and that was just a 1.2 run differential.

Why does this gap matter? xERA takes into account the quality of hitters' contact (exit velocity and launch angle). So, when a pitcher's xERA exceeds their real ERA, it suggests the pitcher may be getting hit hard but is getting lucky. And, with the kind of gap Sugano has, it suggests he is doomed for an eventual regression.

What specifically explains the gap in Sugano's case? One possibility is his low strikeout rate, which sits at 2.89 K/9 and is the worst in all of baseball among 85 qualified starters. Lower strikeouts, of course, means more batted balls in play and higher likelihood of hits and runs.

But a low strikeout rate can't be the only explanation because there are and always have been good pitchers who don't strike a lot of hitters out. So, I pulled a list of four pitchers with similar K/9 to Sugano but lower xERAs this season.

What's really going on with Tomoyuki Sugano? Will his strong start carry into the summer?

Like Sugano, Parker, Lodolo, Severino, and Lugo do not rely much on the strikeout; all five are among the bottom 12 pitchers in K/9.

But their xERAs are much lower than Sugano's because of their low barrel rates. MLB defines barrels as "batted-ball events whose comparable hit types (in terms of exit velocity and launch angle) have led to a minimum .500 batting average and 1.500 slugging percentage."

In other words, barrel rate accounts for all batted balls that fall into a highly successful combination of exit velocity and launch angle. For pitchers, the lower the barrel rate, the better.

So, Sugano surrenders the highest number of barrels among this group of five and the 15th most among 85 qualified. These barrels will eventually turn into more hits, runs, and a higher real ERA, one that is not 2.5 runs less than his xERA.

The other four pitchers compensate for low strikeout rates by inducing fewer barrels, whereas Sugano does not.

It works the same in the opposite direction. Joe Ryan, MacKenzie Gore, and Hunter Greene all have higher barrel rates than Sugano but xERAs below 3.70. How? They each strike out 9.33 or more batters per nine innings, so they offset more barrels with more strikeouts.

Take this as an example: Sugano and Greene each pitch a complete game (this is how you know it is hypothetical), surrendering 5 hits each. Sugano strikes out 3 (2.89 K/9) and Greene strikes out 10 (10.27 K/9). In total, Sugano allows 29 batted balls (27 outs - 3 strikeouts + 5 hits) and Green allows 22 batted balls (27 outs - 10 strikeouts + 5 hits).

That is an additional seven batted balls against Sugano that can result in hits. Multiply that by 20 complete games and that is 140 more batted balls against Sugano than Greene. And, given their nearly identical barrel rates, this will certainly result in more hits and runs for Sugano than Greene.

Perhaps the takeaway here is that pitchers can get away with a low strikeout or high barrel rate but not both — and both are currently an issue for Sugano (71/85 in barrels, 85/85 in strikeouts).

It is still so early into Sugano's MLB career so this can go in a number of directions. Perhaps he will become a strikeout machine and put all of this behind him or maybe he will continue to thrive by averaging two strikeouts per game. Regardless, these trends suggest an impending regression unless Sugano makes some adjustments to his approach.