Scouting the AFL: Red Sox's Kopech shows top-of-rotation potential; Martes' command is off

Hard-throwing right-hander Michael Kopech posted a 2.08 ERA in 12 Class A starts this season, with 86 K's in 56 1/3 innings. Brian Westerholt/Four Seam Images/AP Images

My final update from five days and 10 games spent in the desert scouting the Arizona Fall League:

Boston Red Sox starting pitcher Michael Kopech allegedly hit 103 or 105 mph this summer, according to some media reports, which would make him the hardest-throwing right-handed pitcher we've ever seen. I have my doubts about those figures, especially since Kopech didn't reach 100 mph when I saw him Saturday in Arizona, but he's still a potential top-of-the-rotation starter with huge velocity and the chance for two other plus pitches.

Kopech was "only" 96-99 mph in his outing at Surprise, where he retired all nine batters he faced in three innings of work, throwing strikes but not really commanding the fastball. His slider and changeup were inconsistent but flashed plus, the slider at 85-88 with tight spin, the changeup at 86-89 with a couple that were good enough for the majors, including one he threw at 89 mph inside to a left-handed batter. Kopech cuts himself off a little in his landing but gets enormous extension out over his front side, so that 99 mph may very well look like 105 to a hitter.