This has been a great season for rookies so far — just ask Heath Cummings, who tried to rank just the hitters from this year's class earlier this week — and another potential impact player is set to make his debut Thursday. This time, the Marlins are calling on yet another talented young arm to join their rotation, in the form of top prospect Zac Gallen, who will be starting in Pablo Lopez's spot in the rotation against the Cardinals, the team that originally drafted him.

It's not clear whether Lopez's absence will be a long-term one, but one reporter says Lopez is likely to go on the injured list with a shoulder issue. So, there's a chance Gallen sticks in the rotation, which should be good news for Fantasy players, because he looks like a possible difference-maker this season.

Coming into 2019, Gallen was a good-not-great kind of prospect. He wasn't considered a top-100 option by any major prospect service, and was generally in the back half of the top-10 of a middling Marlins' farm system. He might have been the kind of prospect whose promotion merits a quick mention in a waiver-wire column, like org-mate Jordan Yamamoto

But being the best pitcher in the minors for half a season tends to inflate your stock. Gallen leads all Double-A and Triple-A pitchers with 112 strikeouts — No. 2 has 93. His 1.77 ERA only ranks seventh among 173 in that group, but nobody with a lower ERA is even within 20 innings of him to date. And none have been working in the Pacific Coast League, where his ERA is a 1.10 runs better than the No. 2 pitcher, and his FIP nearly half a run better. 

In fact, it's his production in the PCL that really makes Gallen stand out so much. Here's what he's doing so far, compared to league averages: 

ERA: 1.77 (5.29)
WHIP: 0.71 (1.497)
K%: 33.6 (22.3)
BB%: 5.1 (9.8)

This is an almost comical level of dominance, but it also represents an outlier for Gallen's career. Up until now, Gallen's production has mostly matched up with his scouting reports; good, but projecting as more of a back-end starter. Now, those scouting reports don't match the production, and they might just be out of date. Gallen was sitting in the mid-90s with his fastball and topped out at 97 mph in the spring, a new level for him. That's the kind of jump that can take a pitcher from organizational depth to a real prospect, and Baseball America moved him into their top-100 in a recent update, so there's buy in from the prospect side as well. 

You shouldn't expect anything like his minor-league dominance when Gallen makes his debut Thursday, but Fantasy players should be excited nonetheless.'s latest projections have Gallen posting a 4.10 ERA, 1.27 WHIP, and nearly a strikeout per inning for the rest of the season — something like what Patrick Corbin has done so far. That may not sound super enticing, but Corbin has been a top-50 starting pitcher in Fantasy even in a disappointing season. And that certainly doesn't represent Gallen's upside, which could look something like what we've seen from Chris Paddack in 2019. 

There's a reason he's been near the top of Scott White's top five to stash in his weekly Prospects Report column, after all. Gallen is by no means a sure thing, and it's possible he's just been feasting on overmatched competition in his second turn through Triple-A. It's also possible the Marlins opt to go with Elieser Hernandez and Yamamoto in the rotation over Gallen, if they outperform him. Shockingly, this isn't a team short on possible rotation options.

However, Gallen looks like one of the organization's most talented pitchers, and a big part of their future plans, and as long as he pitches well, he should stick. Ahead of his debut, Gallen looks like a must-add option wherever he's available, so go make sure he's not out there in your league.