Mike Moustakas, 3B, Royals
The Royals were 26-34 on June 9 and in fourth place in the American League Central. Since then, they've been the American League's best team with a 31-20 run that has vaulted them into the second AL wild card spot. The man leading the charge has been Moustakas. The 28-year-old has hit .281 with 17 home runs, 39 RBIs and an .890 OPS during the Royals surge, and become the middle-of-the-order anchor long expected since he was made the second overall pick in the 2007 draft. Overall Moustakas is second in the AL with 32 home runs, a career-high, and ranks in the top 10 in the league in RBIs, total bases and slugging percentage.
Jesus Aguilar, 1B, Brewers
The Brewers keep unexpectedly hanging around the postseason picture, and one of the reasons has been contributions from unheralded players like Aguilar. A 27-year-old rookie who was plucked off waivers from the Indians in the offseason, Aguilar entered Tuesday hitting .272/.332/.505 with 13 doubles, 11 home runs and 38 RBIs in only 238 plate appearances. His .837 OPS trails only Aaron Judge, Cody Bellinger and Trey Mancini among rookies with at least 90 games played.
Jacob Faria, RHP, Rays
Few organizations have a track record of developing homegrown pitchers like the Rays, and Faria is their latest success story. Drafted in the 10th round in 2011 out of high school, the Rays took their time moving Faria up the ladder and made a series of adjustments to his delivery, the latest of which set him up for a breakthrough. Since adding velocity in the offseason, Faria has been a new pitcher. He led the minors in strikeouts when he was called up to the Rays in June and has been dominant since joining them, going 5-2, 2.81 with 67 strikeouts in 67.1 innings to cement himself as a staple of Tampa Bays's rotation moving forward.
Homer Bailey, RHP, Reds
Bailey's return from yet another elbow surgery has not been a good one. Bailey had surgery in February to remove bone spurs from his elbow and returned to the mound in June. He has an 8.86 ERA in nine starts, including his latest ugly outing in which he got rocked for 10 hits and 10 runs in 3.1 innings against the Cardinals. Bailey has pitched only 77 innings the last three seasons due to injury, the repeated surgeries appear to have taken a toll on his stuff. Per Brooks Baseball, Bailey's average velocity on all of his pitches is down 1-2 mph since his last healthy season in 2014, and batters are crushing him. He's allowed a .378 average on fastballs, a .462 mark on his sinker and a .455 average on his slider this year.
Clayton Richard, LHP, Padres
The wily veteran is trying to hang on with his low 90s sinker, but it increasingly isn't working out. Richard has gotten progressively worse as the year wears on, with his ERA in each month jumping. He had a 4.29 ERA in April, 4.36 in May, 5.86 in June and 7.36 in July. Righthanded hitters in particular are having a field day with him, hitting .324/.376/.545 against Richard this season.
Matt Holliday, OF, Yankees
The end of the line appears near for the decorated 37-year-old veteran. Holliday's .229 batting average and .319 on-base percentage are both career worsts, and it's not getting better. He's hit an ML-worst .136 (5-for-81) since July 8, and was placed on the disabled list after tweaking his lower back over the weekend.