MLB Rookie Report: Lucas Giolito, RHP, Nationals

The Washington Nationals have addressed a temporary rotation vacancy by summoning Lucas Giolito from AA Harrisburg, and he'll square off at home against a scuffling Mets offense on Tuesday night.

The consensus top RHP prospect in the game, Giolito gets the surprise call to the Show despite some uneven performances in his second turn through the Eastern League, accentuated by the highest walk rate (4.31 BB/9) of his career.

The Stuff

Make no mistake, the Nats' prized pitcher has the advanced arsenal to pose problems to Major League hitters right away. Giolito generally works 92-96 with his four-seamer, but has an extra gear that will produce triple-digit readings at times. The tape confirms he uses a two-seamer and one industry source even has him cutting the fastball. All iterations of his heater play up because the 6'6" uber-prospect provides plenty of downhill plane in addition to commanding them well.

Giolito's 12-6 'power' curve is the other main attraction, a low 80's bender that can top out as high as 86. He can spot it, bury it, add and subtract to it, and the vertical movement is said to be top-shelf. The ensuing PITCHF/x data will likely tell the full tale of its filthiness.

Most scouting reports indicate that Giolito's changeup flashes plus but needs refinement, as is true with many young pitchers. But J.J. Cooper's freshest take warns us that the change might actually be his preferred offspeed weapon. This is quite the claim considering the prowess of his hammer, but Giolito's recent reverse splits seem to support the notion. Per BA, righthanders are strumming .290/.373/.387 off him in the past two seasons, while he's stymied southpaws to a .192/.295/.238* mark. That he doesn't get a lot of fade on his changeup is a testament to how he's mastering the 'arm speed' part of the equation.

* There's a chance this figure should read '.338', but I don't have the data (i.e. SLG% splits) to verify.

Video courtesy Adam Hayes

The Other Stuff

Add up the particulars and it's hard not to come to the conclusion that Giolito is the best RHP prospect in the game not named Shohei Otani. However, the jump from the Eastern League to the Bigs shouldn't be undersold. Giolito has turned around a rocky start, but to fulfill his potential as a frontline ace there are still improvements needed at the highest level.

The first issue is free-pass related, as Giolito's serving up walks at a higher clip (10.9 BB%) than at any stop in his career. We might pin some of the early wildness on reported mechanical changes that didn't take, but it's something to monitor as he battles more patient hitters.

The second point of emphasis ties in with the first, in that Giolito needs to remain mechanically consistent with his delivery. At a towering 6'6" he's got a lot of appendages to keep in sync, and when he's off with his release and landing his whole arsenal suffers. Batters are hitting .315 off him with RISP this year in a bite-sized 71 inning sample, so he'll need to enhance his approach with runners on.

It's unclear whether this is a one-and-done spot start for Giolito or a legit audition to stick in the rotation. What is clear is that despite Dusty Baker's presence, the Nats under Mike Rizzo have historically enacted a risk-averse plan with their prized assets. That'll be no different this time around, and we shouldn't expect the young righthander to even see the light of day in October.

In the meantime, Giolito is here and has the unquestioned ability to make a Strasburgian impact on the team's postseason chase. He's been marinating in the minors longer than 'Stras' did, and after throwing 117 innings last year we may be able to safely project him for an additional 70 more in 2016.

*Where* he'll throw those innings is the last remaining question. Giolito will begin to answer that query tonight, taking the bump against the rival Mets in his much-ballyhooed debut. If he can spot his electric stuff where he wants it, he might be the rare rookie that wins Dusty's trust and rides it to an explosive second half.