Insider Info From Kervin Castro and Gregory Santos’ Breakout Instructs

Salem-Keizer's Kervin Castro pitches during the home opener against the Boise Hawks at Volcanoes Stadium on Friday, June 14.
Salem-Keizer's Kervin Castro pitches during the home opener against the Boise Hawks at Volcanoes Stadium on Friday, June 14. /
SF Giants, Gregory Santos, Kervin Castro
Salem-Keizer Volcanoes pitcher Gregory Santos is one of the most exciting prospects in the SF Giants farm system. /

SF Giants pitching prospects Kervin Castro and Gregory Santos had breakout instructs. One industry source revealed some exciting numbers to our own Marc Delucchi.

SF Giants prospects Gregory Santos and Kervin Castro were two of the more unexpected names added to the team’s 40-man roster last Friday. However, one industry source told Around the Foghorn, “Castro and Santos both dominated instructional league.” Per the source, both made such major strides that either could have been a top Rule 5 draft target by another organization.

Santos has been one of the hottest prospects in baseball over the past week. Eric Longenhagen of FanGraphs said on a podcast that Santos will be ranked among the top-100 prospects on his list this winter. Baseball America’s Kyle Glaser listed Santos among 19 prospects who impressed at the instructional league as well.

Castro though has not received the same attention. The 21-year old has been considered a sleeper in the system for some time, previously working off a low-90s sinker that generated soft contact at a strong rate. In 2019, he was the ace of the Salem-Keizer Volcanoes working to a 2.66 ERA with a 4.61 K/BB in 14 starts. He has yet to play in full-season ball.

Santos, also 21, made his full-season debut in 2019 with the Augusta Greenjackets, but injuries limited him to just 8 starts. He did manage a 2.86 ERA and posted his best career walk-rate (2.3 walks per nine innings), but also saw his strikeout rate dip to a mediocre 6.75 strikeouts per nine innings.

As a starter, Santos has the stuff to be an effectively wild mid-rotation arm even if his command only reaches a 40 (below-average) grade, which is part of what made the low strikeout rate in 2019 concerning. Santos’ best pitches have been a mid-90s sinker and cutter that pair with a slider that has flashed as plus. His changeup was a recent development that could become a usable big-league pitch but is a long way from reaching that point.

At the instructional league, both Gregory Santos and Kervin Castro showed the best stuff of their career. According to information obtained by Around the Foghorn, Santos’ fastball averaged 98 mph and generated whiffs on 37% of opponents’ swings. Castro’s fastball saw a substantial velocity jump as well, averaging 96 mph and generating a 41% whiff rate.

On top of their increased velocity, both pitchers threw strikes on roughly two-thirds of their pitches, above the MLB average of around 62%. While in line with Castro’s previous performances, Santos had yet to consistently miss bats and throw strikes simultaneously. Needless to say, it is a great sign of development.

SF Giants Developmental Decisions

According to Glaser, Santos pitched entirely out of the bullpen at instructs and was limited to one-inning appearances. Many industry officials, including those cited by Glaser, believe his future will be in relief. However, in conversation with Around the Foghorn, the industry source believes the Giants will give Santos another opportunity to stick in the rotation.

Given the dearth of top pitching prospects in the Giants system, it’s easy to see why they would want to give Santos another opportunity to make it work. If he can carry his instructional league success back into the rotation, he could quickly become the best pitching prospect in the system.

There has been no reporting on whether Castro followed a similar usage regiment or not.

Even if Castro followed more of a starter’s routine, pitchers were limited to shorter outings at the instructional league to lower the risk of injuries and give other pitchers opportunities. With that in mind, seeing velocity jumps is not entirely unexpected. Still, neither Santos nor Castro had shown the ability to consistently generate the velocity they showed.

Santos ranked as the 19th best prospect in the SF Giants organization in ATF’s most recent prospect ranking. Castro was in consideration for the ten best prospects that missed the top 31 rankings. Following instructs, both will see significant jumps in their respective rankings.

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Without a minor-league season in 2020, it has been almost entirely up to players to develop on their own. Both Kervin Castro and Gregory Santos deserve a lot of credit for the steps they took to be ready to return. If minor-league baseball is played in 2021, they will be two of the most intriguing SF Giants prospects to watch.