Georgia has recently been a hotbed of prep talent;, Last year, four prep players from the state heard their name called in the first 40 picks of the draft. Mac Marshall represents another wave of Georgia talent, though the depth of national prep arms has him a little further down on draft rankings than what his talent and upside currently shows.
Marshall is currently ranked #58 by Jonathan Mayo's MLB.com draft rankings. I am sure their draft guys have good reason for ranking him there, but I firmly believe Marshall is a better prospect than that.
Marshall, a lefty, sits in the low 90s with his fastball and can touch 94. Marshall's secondary pitches seem a fairly advanced for a prep arm. Both his curveball and changeup sit in the upper 70s, and the change is a little more advanced than the curveball. Even so, both of these secondaries can grade out as plus pitches at times for Marshall when he's on. The struggle with prep arms is projecting their secondaries and getting them to become consistent pitches (even a guy like Tyler Kolek has these questions). Though Marshall's arsenal is by no means a polished product, he has a better feel for his pitches than most prep arms I've come across this year. If his fastball were a few ticks higher, I think he would be talked about as a slam-dunk first rounder, but touching 94 for a lefty is still pretty solid. The changeup he throws around the :20 second mark of the first video (MLB.com) video below is especially impressive.
Marshall's mechanics are pretty clean. He comes in at a normal angle from the left-side, but his delivery can change a bit when he's throwing his curve. His arm angle gets a bit higher when he throws that pitch, as opposed to the lower, normal angle on his fastball. Maybe nothing to see here, but it's an observation that I came across when watching video on him. On most of his changeups, however, the arm angle was pretty consistent compared to the fastball, an important element of deception for the comparison between the two pitches.
Marshall hasn't gone without exposure; he's from Georgia, a paradise for scouts to watch prep players, and has participated on the Perfect Game and the Team USA prep circuits. I simply believe that the sheer number of other prep arms, all with a bit more velocity (Kolek, Holmes) or big-time upside (Aiken, Toussaint) and the depth of college pitching have continued to keep Marshall down in the rankings. He doesn't presently show either huge velocity or devastating stuff, but his 6'2'' frame suggests that some additional velocity is possible, and his breaking pitches have all the present tools to develop into quality offerings with swing-and-miss ability.
Though it's not clear what the Astros are looking for with their second and third picks in this draft, there's been a lot of talk about a high-upside arm falling to the lottery pick. Marshall could be that guy, and I would be very happy with his selection there.
There's always a high risk with high school arms, but Marshall seems fairly polished. Right now I would project him at the back end of an MLB rotation, but he could be a #2 or #3 starter at the MLB level if his secondary pitches develop nicely. If his fastball velocity increases, he has an even higher projection.
Though he's ranked #58 by MLB.com, Marshall is a little higher on some other publications. John Manuel has him at #33 over at Baseball America. Right now, I see Marshall going in the late first or supplemental round range, but with all the variability of the draft and prep arms taken into account, he could be available when the Astros pick at #37. Don't rule out the Braves, who pick at #32. They're suckers for their in-state prep players (and for good reason). Marshall is committed to LSU but there's nothing to suggest that he won't sign.