Sheffield, 23, has seen brief MLB action in each of the past two seasons. But he hasn’t yet made his first start — a milestone he’ll reach this evening when he takes the ball against the Blue Jays.
While Sheffield’s early appearances in the bigs haven’t been laden with promise, he has long been considered a significant talent. Drafted in the first round back in 2014, he has since headlined a pair of major trades (from the Indians to the Yankees and then on to the Mariners).
At the same time, the lefty hasn’t quite sustained the top-100 prospect hype he carried for the past four seasons. He just doesn’t seem to be showing quite the upside that had once been posited, with some command issues and stagnant K/BB rates over multiple seasons in the upper minors.
The consensus still seems to be that Sheffield will turn into a solid MLB starter, which would work just fine for the M’s. He struggled quite a bit at Triple-A to open the year, allowing a dozen home runs with a middling 48:41 K/BB ratio in 55 innings there. But Sheffield has turned it up since in a dozen Double-A starts, over which he carries a 2.19 ERA with 9.8 K/9 and 2.1 BB/9.
If all goes well, it’s possible Sheffield will position himself for a spot in the 2020 Seattle rotation. It remains to be seen how many innings he’ll be allowed to accumulate down the stretch. Sheffield is already at a career-high 133 in the present campaign, though he’s probably in position to build up further after averaging more than 120 frames per season in the prior three campaigns.