24. Blake Snell, SP, Rays
Bats: Left | Throws: Left
Age: 22 (12/4/92)
2015 levels: high Class A, Double-A
2015 stats: 9-2, 1.28 ERA, 1.09 WHIP, 99 K, 39 BB, 84 2/3 IP
Second-half callup is ... unlikely.

Snell didn't allow an earned run in his first eight appearances this year. And it wasn't all luck; opponents hit just .120 off him during that stretch. He has control issues but has made enormous strides this year and gives the Rays another potential top-of-the-rotation guy.

25. Aaron Blair, SP, Diamondbacks
Bats: Right | Throws: Right
Age: 23 (5/26/92)
2015 levels: Double-A, Triple-A
2015 stats: 8-4, 3.23 ERA, 1.18 WHIP, 83 K, 32 BB, 106 IP
Second-half callup is ... likely.

Blair looked like a breakthrough prospect last year, mixing a mid-90s fastball with a power curveball, but his strikeout rate has dipped considerably this year, raising questions about his upside. At the same time, he did what he needed to do to get to Triple-A, compiling a 2.70 ERA and 1.12 WHIP in 13 starts at Double-A.

Honorable mentions: Orlando Arcia, SS, MIL; Tyler Beede, SP, SF; Dylan Bundy, RP, BAL; David Dahl, OF, COL; Tony Kemp, 2B, HOU; Sean Manaea, SP, KC; Nomar Mazara, OF, TEX; Ketel Marte, SS, SEA; Sean Newcomb, SP, LAA; Peter O'Brien, C, ARI; Stephen Piscotty, OF, STL; Hunter Renfroe, OF, SD; Braden Shipley, SP, ARI; Jameson Taillon, SP, PIT; Jesse Winker, OF, CIN