Castillo was perhaps the prize of this year’s rotating market. After missing a few weeks with shoulder soreness to open the year, Castillo made his season debut in early May and looked like a bona fide leadoff arm. He made 14 starts and worked 85 innings, posting a 2.86 ERA despite playing his home games in one of the friendliest parks in the league. Castillo struck out a quality 25.8% of opposing hitters against a solid 8% walk rate. This season’s 47.1% percentage is down a bit from his 2019-21 levels, but remains a few points better than the league average. That kind of high-end production is about what we’ve come to expect from Castillo, who has established himself as one of the sport’s top arms in recent seasons. He has posted an ERA under 4.00 in each of the past four years, posting a cumulative 3.49 in 91 starts since the start of the 2019 campaign. That ranks 24th among 98 eligible players in that division . His 26.8% strikeout rate ranks 23rd on this team and is 12th with a 14.2% swinging rate (whistles per pitch). He has completed the strikeout with a whopping 54.8% ground ball rate which ranks in the top ten. Few pitchers can match Castillo’s combination of forehands and pitches, and the 29-year-old backs it up with an impressive arsenal. He is one of the toughest starters, averaging just 97 MPH on both his square and sinker. Castillo’s secondary pitch, his changeup, is among the top off-speed offerings in the game, and he also has strong results on his slider. Castillo will move to the front of a rotation that suddenly looks to be one of the scariest in the sport. The M’s signed AL Cy Young winner Robbie Ray to a five-year deal over the winter, and second baseman Logan Gilbert has a 2.78 ERA through 21 starts. Rookie George Kirby, who was generally considered among the top prospects entering the season, has a 3.50 ERA in his first 13 big league outings. Chris Flexen and Marco Gonzales aren’t high-strike weapons, but they’re more than capable back-of-the-rotation guys. Seattle will want to keep an eye on the attendance totals for Gilbert and Kirby, so adding even a solid back arm would be advisable. Instead, president of baseball operations Jerry Dipoto and his staff have made bigger moves to bolster the 54-46 club they expect to snap the franchise’s two-decade playoff drought. Should they make the postseason, the front office and fanbase will no doubt feel strongly about their ability to match up against opponents’ top three arms with Castillo, Ray and Gilbert. The deal extends beyond the 2022 season, as Castillo will be eligible for arbitration for the final time this winter. He earns $7.35 million this year, about $2.75 million of which has yet to be paid. He’ll earn a decent raise in arbitration, but he’ll still command an abundantly affordable salary — likely around $12M. That’s an obvious bargain for a pitcher of his caliber, making a year and a half of his services incredibly valuable. This is reflected in the return, which looks very strong. Marte and Arroyo were the top two prospects in Seattle’s system in Baseball America’s most recent top 100, ranking 47th and 48th in the league, respectively. Marte, the best-known of the group, entered the season ranked among the top 15 farmhands in the game as rated by each of Keith Law of the Athletic, FanGraphs and ESPN’s Kiley McDaniel. A 6’3″ outfielder from the Dominican Republic, Marte is projected worldwide as a prospect and power hitter capable of hitting 25 or more homers per year at his peak. He has played shortstop exclusively in the minors, and while evaluators suggest he could eventually move up at that position, he’s expected to remain in the infield as a potential above-average third baseman.He spent the year in High-A as a 20-year-old, putting up an impressive .270/.360/.460 line with 15 homers, a strong 10 walk percentage, 8% and a manageable 21.1% strikeout rate through 389 plate appearances . Arroyo, 18, was Seattle’s second-round pick in last year’s draft. The Puerto Rico native has already raised his stock significantly in his first full pro season, posting a .316/.385/.514 clip in Low-A. He has collected 13 homers and 19 doubles and has stolen 21 bases. That kind of offensive performance was unexpected, as the switch-hitter entered the season more highly regarded for his ability and defense at shortstop than his bat. Stoudt recently checked in as the M’s No. 10 prospect, per Baseball America. The 24-year-old righty pitched in Double-A this year, pitching to a 5.28 ERA in 87 innings. He has a slightly below-average 22% walk rate and a paltry 5.9% walk rate that look more palatable, though. BA writes that he works in the 94-98 MPH range with his fastball and has a steady stream of secondary offerings, led by his changeup. The 2019 3rd round pick would have to be added to the 40-man roster this offseason to avoid being selected in the Rule 5 draft. He is viewed as a potential starter. Moore, not to be confused with the former Seattle player of the same name, was a 14th-round pick out of junior college last year. The 22-year-old righty has worked exclusively out of the bullpen in Low-A, posting a 1.95 ERA in 32 1/3 innings with a ridiculous 43.6% strikeout rate. He generally faces younger competition and has walked nearly 13% of opponents, but BA recently wrote that he possesses a 95-97 MPH fastball and a swing-and-miss breaking pitch. He’ll add an interesting low-end arm to Cincinnati’s system. The trade — which marks the second time in four months these two teams have lined up in a blockbuster — will have many ramifications. Seattle’s decision to move arguably its top two prospects for one of the best starters in the sport reinforces that the M’s see themselves as a legitimate contender in the American League. It also seemingly means Juan Soto is out, though there is still plenty of top-level talent for Dipoto and his team to further bolster the roster over the next three days. Second base looks like a potential target area, as does backup catcher. Castillo, however, appears to be the splash — the impact designed to put a team that is generally strong around the diamond over the top. As for the Reds, it’s the second (and likely most notable) trade they’ll make this week as they strip the big league roster in search of future talent. Castillo’s former rotation partner Tyler Male could soon join him and be brought in for a flashy comeback (though not as strong as this one). Rental players like Brandon Drury and Donovan Solano won’t recoup a franchise-changing package, but there’s no reason for them not to join Tyler Naquin and Castillo in switching clubs. With Castillo off the market, Mahle and A’s pitcher Frankie Montas become the top two rotation candidates, aside from a handful of high-performance arms who may be available despite having control windows that extend beyond 2023 .Teams like the Yankees, Cardinals, Rangers and Twins are known to be in the market for rotation help. MLB.com’s Mark Feinsand tweets that 12 teams have been in contact with the Reds for Castillo and suggests the Yankees’ offer was close to Seattle’s quality. The Athletic’s Ken Rosenthal indicates that Texas also made a strong push. In the end, the Mariners put the best offer on the table, leaving many others to look elsewhere over the next 72 hours. ESPN’s Jeff Passan was the first to report that Seattle was closing in on a deal for Castillo. Ryan Divish of the Seattle Times was the first to report the prospect of a return to Cincinnati. Image courtesy of USA Today Sports.
