Known as the graduate school of the Minors, some of baseball's best have gone through the Arizona Fall League prior to starting their big league careers. 
Don't believe me? 19 former Most Valuable Players have competed in the league along with six Cy Young award winners. Heck, this season alone is ripe with former Fall Leaguers competing for baseball's biggest awards.
Christian Yelich ('12), Cody Bellinger ('16), Anthony Rendon ('12) are all vying for the National League MVP nod while in the American League, Mike Trout ('11), appears to have run away with the award. Forty-three 2019 Major League All-Stars were Fall Leaguers and Rookie of the Year favorites Yordan Alvarez ('17) and Pete Alonso ('18) are alum as well.
What is this hidden gem? The Arizona Fall League is a six-week-long season operated out of four spring training facilities in the desert after the Minor League schedule has concluded. It gives players a chance to compete against the best players in the Minor Leagues and prove they are ready for the next step.
Reno Aces' infielder, Andy Young, used the Fall League to break out in a big way in 2018. In 20 games, he hit .301 with three home runs, 15 RBIs, and 13 runs scored to go with a .936 OPS. The performance shot Young up baseball's prospect rankings so high he was seen as a valuable piece to the Arizona Diamondbacks' 2018 trade that sent franchise player Paul Goldschmidt to the St. Louis Cardinals. 
Young appears to be in the future plans for the D-backs as he hit .280 in 68 games this season with Triple-A Reno. He played every infield position but first base for the Aces and launched 21 home runs, drove in 53 runs, and scored 53 times.
This season, the D-backs are sending seven prospects to the Fall League with a few that you may see in Reno as early as 2020.

Seth Beer 
Pos: OF Bats/Throws: L/R Ht: 6' 3" Wt: 195 Age: 22 Acquired: 2019 Trade (HOU) MLB Pipeline Rating: D-backs' No. 4, Overall No. 95
Seth Beer was brought to the organization in the 2019 trade deadline trade that saw Zack Greinke become a Houston Astro. Beer's name may catch peoples' attention, but his play on the field is really what we should be talking about. The lefty is the Diamondbacks' top prospect competing in the Fall League this season coming in as the organization's No. 4 player according to MLB Pipeline. 2019 was his first full season in professional baseball after being selected in the first round out of Clemson in 2018. With High-A Fayetteville, Double-A Corpus Christi, and Double-A Jackson this year he combined to hit .289 (130-for-450) with 26 home runs, 103 RBIs, 72 runs scored, and 24 doubles to go with a .516 slugging percentage. At just 22-years-old, Arizona could be patient as Beer still has some strikeout issues to work through but I'd expect to see the slugger in Reno at some in 2020 if he remains hot at the plate. 
Matt Peacock 
Pos: RHP Bats/Throws: R/R Ht: 6' 1" Wt: 180 Age: 25 Acquired: Round 23, (2017, ARI)
Matt Peacock battled injuries in 2018 splitting time between Single-A Kane County and High-A Visalia. He threw a combined 98.2 innings compiling a 7-6 record and 4.20 ERA. 2019 was a breakout year for the 25-year-old in Jackson. He was the ace of the staff throwing 115.1 innings while notching an 8-4 record and 2.97 ERA with 81 strikeouts. Starters Alex Young, Taylor Clarke, and Jon Duplantier all have Minor League options left so we may see them again in Reno next year, however, for the time being, they have graduated to the Major Leagues meaning the squad will be looking for starting pitching next year. Peacock throws a heavy sinker which will bode well in hitter-friendly Greater Nevada Field. 
Miguel Aguilar 
Pos: LHP Bats/Throws: L/L Ht: 5' 11" Wt: 180 Age: 27 Acquired: Free Agent 2017 
Miguel Aguilar spent the first five seasons of his professional career playing in Mexico before signing with Arizona in 2016. The lefty reliever has been a stopper out of the bullpen since arriving in Visalia in 2017. He held hitters to a .197 batting average that season with a 1.19 ERA over 22.2 innings during his first season. In 2018, he threw 57.2 innings across High-A Visalia and Double-A Jackson with a very respectable 2.97 ERA and 65 strikeouts. This past season in Jackson, Aguilar posted a 2.12 ERA over 29.2 innings. He struck out 33 and held batters to a .208 average. With Jimmie Sherfy graduated to the big leagues and out of Minor League options, the Sonora, Mexico native is an early candidate to close games for the Aces next season. 
Matt Brill
Pos: RHP Bats/Throws: R/R Ht: 6' 2" Wt: 190 Age: 24 Acquired: Round 12 (2017, ARI)
Drafted out of Appalachian State in the 12th round in 2017, Matt Brill has ascended quickly through the D-backs' Minor League system ending up in Double-A Jackson this season. A hard-throwing righty from Illinois, Brill is a reliever prospect. He's a strikeout threat anytime he takes the mound as he sat down 143 batters in 117.1 innings pitched over his Minor League career. At 24-years-old, he's a possibility to be promoted to Triple-A Reno next season.  
Cody Reed
Pos: LHP Bats/Throws: R/L Ht: 6' 3" Wt: 245 Age: 23 Acquired: Round 2 (2014, ARI)
Cody Reed is using the Arizona Fall League to make up for lost time. He missed all of 2018 with an arm injury and threw just 13 innings in 2019 in Rookie Ball and Short Season Hillsboro. Measuring in at 6-foot-3 and 245 you'd expect Reed to clock in as a power pitcher. However, the 2014 second-rounder is a crafty lefty that uses a slider as his strikeout pitch. Until we see how he responds from injury, he is a tough case to predict. Reed has been quality while he's been healthy holding a 20-22 record with a 3.14 ERA while striking out 351 batters over 320.2 innings pitched in his Minor League career. 
Geraldo Perdomo 
Pos: SS Bats/Throws: S/R Ht: 6' 2" Wt: 184 Age:19 Acquired: Free Agent 2016 MLB Pipeline Rating: D-backs' No. 7
At just 19-years-old, Geraldo Perdomo appears to be a long way away from the upper levels of the Minors. However, he's got massive upside. MLB Pipeline says Perdomo is possibly the best defensive prospect in the D-backs' system. 
"He's a tall and rangy shortstop who has the actions, hands and plus arm strength needed to remain at the position, and he's universally praised for his instincts and internal clock," MLB Pipeline said.
Perdomo may be recognized for his defense, but he is no offensive slouch. The 6-foot-3 switch-hitter hit .275 over 116 games for Class-A Kane County and High-A Visalia this year. The speedster stole 26 bags and got on-base at a .397 mark as well.
Jake McCarthy  
Pos: OF Bats/Throws: L/L Ht: 6' 3" Wt: 195 Age: 22 Acquired: Round CBA (2018, ARI) MLB Pipeline Rating: D-backs' No. 28
Last but not least comes outfielder Jake McCarthy. The lefty is known for his advanced approach at the plate after spending three seasons at the University of Virginia. The former first-rounder battled some injuries in 2019 and appeared in just 53 games for High-A Visalia batting .277. Another speedster in the D-backs' system, McCarthy stole 18 bags in his limited time last season and profiles as an everyday centerfielder moving forward. Arizona's No. 28 prospect is definitely someone to keep an eye on in the coming years.