After Bryce Miller spent much of Spring Training competing for a spot in the Mariners’ big league rotation, it might have surprised some to see him start the year back in Double-A, where he had finished so strongly in 2022, rather than a bump up to Triple-A. 

The Mariners proved on Monday that Double-A Arkansas is also only a phone call away when they summoned Miller, their No. 2 prospect (No. 88 on MLB Pipeline's Top 100 Prospects list), to make his big league debut on Tuesday. And much like with his starting assignment, perhaps some on the outside looking in were a bit shocked the M’s called upon the right-hander after he posted a 6.41 ERA over his first four starts.

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Aside from 19 2/3 innings being way too small of a sample size to discount what he did in his first full season after the Mariners took him in the fourth round of the 2011 Draft out of Texas A&M (133 2/3 IP, 11.0 K/9, 1.04 WHIP, .195 average-against), there are also more behind-the-surface stats for the start of his 2023 season.

The 24-year-old right-hander is coming up with some wind behind his sails. His last start for Arkansas was his best, when he gave up just one hit, one walk and a run in five innings, striking out five. The other three outings don’t look as pretty on paper, but rest assured, he’s not getting called up because of that one strong appearance.

Miller had a legitimate four-pitch mix, starting with a high-spin fastball that averaged 95 mph and touched triple digits in Double-A last year. His hard slider was a true out pitch at times and provided a different look with a slower, truer curve, and both breaking pitches missed bats. His changeup featured some impressive sink and he did a good job of getting ground-ball outs as well.

But that was last year, you might proclaim. He clearly hasn’t been as sharp this season. Au contraire. This is where the numbers you see online don’t match his performance. Miller's stuff has been just as electric, just as precise. His four-seamer has been 95-99 mph with plus command and at least plus ride up in the zone. That 86-89 mph slider has plus action and he can throw it for strikes to hitters on both sides of the plate. He’s scrapped the curve for a distinct "second slider," a sweepy pitch across the bottom of the zone that acts as a premium swing-and-miss pitch. The changeup is an upper-80s above-average offering with depth and fade. 

If there’s one area of concern, it’s been the long ball. Miller gave up five homers over those four starts. There’s some concern that left-handed hitters have seemed pretty comfortable against him.

But it’s a small concern because the Mariners have internal pitching grades for every arm in the system that take velocity, movement and location into account. Those indicators have Miller as the best pitcher in the system, not just in that last start, but all year. Call it some bad luck, call it the way baseball goes sometimes. Based on internal metrics, Miller graded out as the best option if and when there was a need in the big league rotation.

That need arose when Robbie Ray was lost for the season. And Miller will be given a fairly long leash to hold onto the spot. They have every confidence he’ll do just that, given that his pitch quality and command have been, in many ways, better than they've ever been. He walked just three in those 19 2/3 innings to bring his career BB/9 rate down to 2.8. 

The amazing thing is people once thought Miller was destined for the bullpen long-term because he struggled with his command and had such a high-tempo delivery. He had spent two years as a reliever at Texas A&M and had mixed results in the Aggies’ rotation in 2021. But the Mariners seem to know a thing or two about developing starting pitching, which is no small feat. They’ve shown they know how to work with young hurlers in the big leagues. Logan Gilbert made 24 starts in 2021, and while he finished with a 4.68 ERA, it paved the way to an even better 2022. George Kirby made 25 starts last year and is off to a very strong one this year. There’s no reason to think Miller can’t, or won’t, follow in the same path and provide another strong mainstay in a playoff-caliber rotation.