*Restricted to only five this week.
Wei-Yin Chen, SP, Baltimore Orioles
Chen has stumbled to the finish line, going 2-5 with a 5.34 ERA over his last 10 starts. However, he still managed to finish the season with 32 starts under his belt, more than any other AL rookie. Of those, 17 were quality starts.
His 4.02 ERA may look mediocre, but what's important in Chen's case is that he never climbed too high above or below the 4.00 mark. For much of the season, he was a model of consistency.
Scott Diamond, SP, Minnesota Twins
Diamond had starts here and there in which his sinker wasn't quite sinking enough, but his rookie season will go into the books as a success. In 26 starts, he compiled a 3.54 ERA while winning 12 games for a bad Twins team. He logged 16 quality starts, one fewer than Chen in six fewer starts.
Kelvin Herrera, RP, Kansas City Royals
There's a reliever in the top five, but I wanted to include at least one reliever in the honorable mentions section as well. With all respect to Robbie Ross and his 2.24 ERA, the second-best rookie reliever in the AL this year was Kelvin Herrera. He led all AL rookies with 76 appearances, posting a 2.35 ERA and a solid 8.22 K/9.
Will Middlebrooks, 3B, Boston Red Sox
After Mike Trout and Yoenis Cespedes, the rookie position player in the AL who made the biggest impact this year was Will Middlebrooks. He only played in 75 games, but he managed to hit .288/.325/.509 with 15 homers and 54 RBI. Per FanGraphs, Middlebrooks still ranks third among AL rookie position players in WAR despite being out since early August with a broken wrist.
Tommy Milone, SP, Oakland A's
No rookie pitcher in the American League was more overlooked this season than Milone. He made 31 starts and won a team-high 13 games with a 3.74 ERA. Only Chen and Yu Darvish logged more innings among rookies, which is a key reason why Milone ranks third among AL rookie hurlers in WAR, according to FanGraphs.