The Red Sox have a high-quality farm system, one that has graduated a number of compelling, relevant prospects such as Mookie Betts and Xander Bogaerts over the past couple of years, with another, Blake Swihart, a little bit ahead of schedule thanks to injuries to Boston's catchers. All of that hasn't diluted the top-end of their talent pool, though, thanks to three major acquisitions made since the summer of 2013: Keith Law has recognized all three of these prospects as three of the very best in the game right now in his in-season update to his top 25.
These three are Yoan Moncada (ranked 11th), Rafael Devers (14th), and Eduardo Rodriguez (18th). None of these players were drafted by the Sox, as Moncada was signed to a record-breaking international deal before the 2015 season, Devers was Boston's major international free agent signing of the 2013-2014 signing period, and Rodriguez was a deadline acquisition from the Orioles last July. It's a credit to the Sox that they were able to replenish the top-end of their farm so quickly and effectively with the resources they had on hand, outside of the draft: in the case of Moncada and Devers, it was money, and for Rodriguez, it was a willingness to give up impending free agent and impact reliever, Andrew Miller.
Moncada just arrived in Low-A Greenville recently, and while he's a second baseman now, that might not be the case forever -- and not just because Dustin Pedroia is the man at second in Boston until such time he is not. Law thinks it's possible Moncada is better-suited to third base anyway, with the more sure thing about Moncada's future being his ability to hit for both average and power.
As for Devers, who is teammates with Moncada on the Drive, there is no shortage of good things to say about his bat. He's just 18, and in his first year of full-season ball, and is destroying every pitcher he faces. While his first week wasn't so great, with Devers posting a .222/.241/.259 slash, he's been nigh unstoppable since: the teenage lefty is hitting .355/.393/.527 with 13 extra-base hits and strikeouts just 16 percent of the time in his 28 games since.
It's unclear where Devers will play defensively in the long run -- he's a third baseman now, but an outfield corner or first base could be in his future as he ages and grows. For that reason, ranking him 14th already seems aggressive. With that being said, though, there is serious potential here with the bat, and Law is known to favor upside, so an 18-year-old who looks like he could shoot through the system to become a middle-of-the-order bat is precisely the kind of player he'd point to early rather than late.
Rodriguez, you're all likely more familiar with, especially since he seems to be the next-in-line option to replace Joe Kelly (or whomever needs replacing next) in the Red Sox rotation. The Orioles dealt him after a ho-hum first half of the season at Double-A, but since the swap, Rodriguez's change-up has improved to the point where Law calls it plus, his slider has found more and better usage, and his fastball command has taken a step forward. He's still just 22, he's left-handed, and he might be capable of competent big-league pitching as of this writing. He needs his command for all of his pitches in order to stick as a starter and ascend to or near the top of a rotation, but if he does, you'll understand precisely why Law thinks so highly of him.