The Red Sox already added a spark to their lineup by promoting one of the top prospects in baseball in August. Andrew Benintendi took over in left field and hit .324/.365/.485 in 21 games before spraining his left knee a week ago.
With big league rosters expanding to 40 for September, Boston is hoping to get similar impact by calling up the game's best prospect. Infielder Yoan Moncada, ranked No. 1 on MLBPipeline.com's Top 100 Prospects list, will join the Red Sox on Friday in Oakland.
Signed at the cost of $63 million ($31.5 million bonus, $31.5 million in a matching penalty for exceeding international bonus-pool limitations) as a second baseman, Moncada is expected to get the bulk of his playing time at third base, where he played his last 10 games in Double-A. Boston's third basemen have compiled baseball's third-worst OPS (.704) at the position, with Travis Shaw (.629 OPS) and Aaron Hill (.513 OPS) slumping mightily since the All-Star break.
• Red Sox's Top 30 Prospects list
The most hyped teenager to defect from Cuba since Jorge Soler, Moncada nearly doubled the bonus record for an amateur player (Aroldis Chapman's $16.25 million in 2010). Often compared to Robinson Canó with more speed, Moncada has outstanding all-around tools and has met all expectations so far. At age 21 this year, he has batted a combined .294/.407/.511 with 15 homers, 45 steals and 72 walks in 106 games between high Class A and Double-A. His power production has increased as he has risen through the Minors, and he slammed 11 homers in 45 Double-A games after hitting 12 in his first 142 pro contests.
Moncada already has starred in front of a national TV audience, earning MVP honors at the SiriusXM All-Star Futures Game in July. After making a nice defensive play at second base to retire the speedy Benintendi and showing off his own quickness with a stolen base, he delivered the game-winning homer by driving a hanging Anthony Banda (Diamondbacks) changeup 406 feet into the upper deck in left field at Petco Park.

A switch-hitter, Moncada has electric bat speed and is dangerous from both sides of the plate. He has made notable improvements in his second pro season, adding more lot to his swing and more patience to his approach. Moncada's home run percentage per at-bat has risen from 2.6 in 2015 to 3.7 (6.2 in Double-A) this year, while his walk percentage per plate appearance has increased from 11.6 to 14.6.
Moncada's best pure tool is his speed, which is well above average and earns 70 grades on the 20-80 scouting scale from some evaluators. He knows how to use it on the basepaths, where he has the acumen to steal a lot of bases with a high success rate (86 percent in pro ball). Moncada has been slowed, however, since spraining his left ankle in early August, and he attempted only one steal in 11 games after his return.
Few players can match Moncada's offensive potential. He projects as a .280 hitter with 20 homers and 40 steals in his prime. While Moncada won't deliver those numbers right away, he should be an upgrade over Shaw and Hill.

Moncada's strong arm gives him a fourth plus tool. He's certainly athletic enough to play second base, though that's unlikely to happen in Boston with Dustin Pedroia signed through 2021.
Though Moncada had played third base in Cuba, he didn't see any time there in the Minors before Aug. 12. He made two errors in his second game there, but he also made some highlight plays. As Moncada gains more experience, his arm and quickness should allow him to become at least a solid defender at the hot corner.
The Red Sox pledged to develop Moncada patiently after signing him, yet his prodigious talent couldn't be denied and he'll arrive in the Majors before the end of his second pro season. While he won't be a superstar right away, he should be an offensive and a defensive upgrade over Shaw and Hill, giving Boston a boost as it chases an American League East title and an AL Wild Card berth.