Previewing Must-Watch Red Sox Prospects in Upcoming Fall League Action

The 2014 season is about to come to a close for the Boston Red Sox, but not every one of their players will be heading home for the winter. 

The Sox have relied on a plethora of prospects in 2014, and not always to great effect. Yet the Sox still have an intriguing core of young players in the majors and upper minors who should factor in prominently to Boston's plans for 2015 and beyond. Given all of the competition for playing time in Boston's system right now, not every player gets all the at-bats or innings pitched that he ideally should.

Thankfully, the Arizona Fall League and Puerto Rican Winter League provide players with a platform in which to gain more experience in between MLB seasons. Often used as a showcase for prospects who are close to the majors, missed time with injury or are simply deemed to require more reps, AFL ball in particular often pits some of the most exciting young players in the game against one another. 

This season, the Red Sox are sending seven players to their AFL affiliate, the Surprise Saguaros, a team they share with the Seattle Mariners, San Diego Padres, Cincinnati Reds, Texas Rangers and Tampa Bay Rays. With that in mind, let's take a look at the five most interesting Red Sox prospects who will see some playing time this fall and winter. 

Rusney Castillo, CF

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Castillo figures to be one of the more exciting players to grace the Arizona Fall League this offseason. The 27-year-old outfielder has yet to truly make his mark on stateside baseball, but he should start 2015 with the Red Sox's MLB club, so he must gain all the experience he can over the next few months.

The recently signed Cuban outfielder has recorded just 16 MLB plate appearances thus far and received limited experience in the minor leagues this season. This comes after a nearly two-year layoff for Castillo when it comes to seeing game action, so the extra reps he gets in the AFL will be welcomed.

Castillo's speed is obvious, and he's already used it to notch his first MLB steal and make some exciting plays in center field. We've yet to truly see Castillo's ability to hit for power, though he did lead off the Triple-A championship game with a homer.

The Red Sox saw firsthand what even a modest layoff in playing time can do to a player when Stephen Drew so badly struggled earlier in the year. There's no reason to think Castillo will suffer the same fate, but at the same time, it's likely to take him some time to get back into the swing of playing every day.

Fall League and Winter League stats don't mean much, but keep an eye on how Castillo performs in the AFL and Puerto Rican Winter League this offseason.

Keith Couch, RHP

Kelly O'Connor, www.sittingstill.net

Couch has flown under the radar during his time as a Red Sox prospect, and for good reason. He doesn't have the upside of any of Boston's better-known starting prospects, and he's ascended somewhat slowly through the minor league ranks.

However, the 24-year-old right-hander had a solid season for Portland in 2014. He posted a 2.96 ERA in 100.1 innings across 17 starts and one relief appearance, and Couch did an excellent job limiting his walks and homers allowed. He didn't miss many bats, but otherwise, Couch excelled.

Given the plethora of young pitchers ahead of him in Boston's system, it’s unlikely that Couch will reach the majors as a starter. His arsenal features a low-90s sinking fastball, an average curveball and a changeup that "tends to float," according to SoxProspects.com, which means Couch doesn't really have an out pitch.

We've seen Brandon Workman, Anthony Ranaudo, Allen Webster and Rubby De La Rosa all struggle in the majors this year, though, and highly touted prospects don't always make the best major leaguers. Couch has positioned himself to see Triple-A at some point in 2015, and from there he'll just be a stone's throw away from the majors.

Sean Coyle, INF

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In a shallower organization, Coyle would probably get more of a billing as an interesting prospect. He's often lost amid flashier names in the Red Sox's system, but Coyle started to get some national recognition in 2014 when he was named to the Futures Game.

A 5'8" second baseman with a compact swing, Coyle naturally draws unfair comparisons to Dustin Pedroia. Despite his natural position of second base and his small stature, Coyle is a fairly dissimilar player from Boston's current second baseman.

Coyle has some pop in his bat and is a better runner than Pedroia, but he doesn't have the same sort of hit tool. That being said, Coyle hit .295/.371/.512 in 384 PA in Portland this season, though according to FanGraphs, that line was bolstered by a .362 BABIP.

Coyle's also suffered through several injuries in his MiLB career, and he missed some time with hand and hamstring issues again in 2014.

Thanks to the presence of Pedroia and Mookie Betts, the Sox started experimenting with Coyle at third base this season. He's a good enough natural athlete to play the position, but as MLB.com points out, his arm doesn't profile terribly well there.

While Coyle has a fairly unique profile as a second/third baseman with pop, his bat very well could carry him to the major leagues in fairly short order. Look for him to gain experience at a few different spots in the AFL this fall, with an eye toward opening up 2015 in Pawtucket.

Aaron Kurcz, RHP

Kelly O'Connor, www.sittingstill.net

Kurcz was part of the return the Red Sox received from the Chicago Cubs in the Theo Epstein deal, and he started to pay some dividends for the Sox in 2014. Kurcz struck out 54 batters in 42 innings as a reliever in Portland, and while he walked too many batters, he didn't give up a homer all year.

The 24-year-old can be forgiven for not showcasing elite command in 2014, however, as it represented his first season back from Tommy John surgery, which robbed him of his entire 2013 campaign. Now healthy and missing bats, Kurcz could shoot through the upper minors fairly quickly.

Listed at just 6'0" and 175 pounds, Kurcz is a bit undersized for a pitcher. He can reach 95 mph with his fastball, however, and mixes in a slurvy breaking pitch and a changeup in his arsenal as well, according to SoxProspects.com.

The Red Sox have plenty of options when it comes to potential prospect relievers, and reliever prospects generally don't garner much attention when in the minor leagues. Yet if Kurcz can develop into a viable sixth- or seventh-inning option at the MLB level, the Sox should consider that a player-development success.

Deven Marrero, SS

Gerald Herbert/Associated Press

Few Red Sox prospects had such an up-and-down campaign in 2014 as did Marrero. The 24-year-old shortstop turned heads in the first half of the season, hitting .291/.371/.433 in 307 PA in Portland and earning a midseason promotion to Pawtucket.

Marrero has long been lauded for his glove, and his offensive explosion in Double-A seemed to suggest he was becoming the type of complete all-around player who could reasonably start for a first-division ballclub. His patience and modest uptick in power served as promising signs.

Yet Marrero was as bad in Triple-A as he was good in Portland. The former first-rounder hit just .210/.260/.285 in 202 PA, playing himself out of any chance of a September call-up.

Marrero's defense may be ready for the majors—MLB.com cites him as a "tremendously instinctive" shortstop—but his offense and baserunning clearly aren’t. In addition to his woes at the plate, Marrero was just 16-for-24 in stolen base attempts this season.

With Xander Bogaerts firmly entrenched as Boston's shortstop of the future, Marrero could be preparing for a role as the Red Sox's utility infielder. He still has a chance to become something more, of course, but he'll need to make some drastic improvements with the bat first.