Ronald Martinez/Getty Images
Scott Diamond, SP, Minnesota Twins
As recently as August 18, Diamond had an ERA under 3.00. In five starts ever since, he has an ERA over 7.00 and has been knocked around to the tune of a .315 opponents' batting average, one that comes complete with a slugging percentage of .583. Diamond could be out of the AL ROY picture altogether by the end of the season if he keeps this up.
Sean Doolittle, RP, Oakland A's
Doolittle isn't having a great month of September, but he still has a solid 3.35 ERA and he ranks second among AL rookie relievers in K/9 at 12.19. His 1.37 FIP is better than that of Aroldis Chapman, according to FanGraphs.
Kelvin Herrera, RP, Kansas City Royals
Herrera leads all AL rookies with 70 appearances this season, and he's sporting a 2.40 ERA and a solid 3.79 strikeout-to-walk ratio. He's just one part of a very exciting Royals bullpen.
Hisashi Iwakuma, SP, Seattle Mariners
A new addition to this week's list, Iwakuma finds himself in the ROY discussion because he's 5-4 with a 2.84 ERA since moving into Seattle's rotation in early July. With Felix Hernandez struggling, Iwakuma may be the best pitcher the Mariners have right now.
Will Middlebrooks, 3B, Boston Red Sox
Middlebrooks has been out of action for well over a month at this point, but his .288/.324/.509 triple-slash line, his 15 home runs and his 54 RBI in just 75 games make him at least worthy of an honorable mention.
Jesus Montero, C/DH, Seattle Mariners
Montero is hitting just .167 over his last seven games, and that's in no small way thanks to his 0-for-8 showing in Seattle's 18-inning loss to the Orioles on Tuesday night/Wednesday morning. Still, only Mike Trout has played in more games than Montero among AL rookies, and Montero's offensive numbers are badly skewed by his performance at Safeco Field. He's a .214/.257/.332 hitter at home and a .305/.337/.453 hitter on the road.
Robbie Ross, RP, Texas Rangers
Ross made his first appearance off the disabled list on Tuesday, and it went well. He pitched an inning against the Angels, allowing no hits or runs and striking out one. Garden-variety stuff for him. His 1.75 ERA leads all AL rookies.