It’s very hard to trade a superstar player and the face of the franchise, but the Diamondbacks pulled the trigger on that deal on December 5, 2018. The Dbacks traded franchise icon Paul Goldschmidt to the St. Louis Cardinals for catcher Carson Kelly, starting pitcher Luke Weaver, minor league infield prospect Andy Young, and a Competitive Balance B Pick (75th overall, Dominic Fletcher). To add insult to injury, the Cardinals extended Paul Goldschmidt for what was considered a team-friendly 5-year, $130M contract before the season started. The Diamondbacks elected to go with MLB controllable players in the deal vs. top-end talent in the Cardinals farm system, which drew criticism about the team’s decision making.
It made sense to trade Goldschmidt: He’s 31 years old and had two horrific slumps to bookend the 2018 season. They were not going to extend him long term and for a small to mid market club like the Dbacks, it’s best to make that move a year early than let him walk for merely a Top 35 draft pick. The strikeout and walk rates declined from his 5-year peak (2013-2017) along with losing a step on defense although he was still above average. The Dbacks elected to trade while he still had a high value, coming off a 5 WAR season, to help build the roster for the present and future. Fast forward 84 games, and it looks like the Dbacks not only won the Paul Goldschmidt trade but completely fleeced the Cardinals on this deal. Goldschmidt has declined into simply an average regular as his bat speed has taken a major step back and his XBH power (his HR total is normal but his singles and doubles have severely dropped) has evaporated as a result.
While he Jean Segura and Mitch Haniger for Taijuan Walker and Ketel Marte swap serves as an excellent reminder that it’s often too early to judge a trade with just half a season in the books, it’s hard to envision a scenario where the Cardinals come on top on this deal overall. The previous aforementioned trade included young talent such as Walker, Haniger, and Marte, three guys who were scratching the surface of their potential at the time, where contributions are a bit harder to project. In that deal it turns out the best player from that trade has ultimately been Marte himself although the Mariners have gotten excellent value from Haniger and Segura as well, a rare case where you can say both teams won big.
With that in mind, let’s break down how the trade has worked in the Diamondbacks favor with the stats updated through June 28th:
Walker was already on the Diamondbacks roster when this trade happened, but he was the one who benefited the most from Goldschmidt’s departure. Walker has established himself as the primary 1B, posting a .260/.331/.484 slash (108 wRC+) while providing above average value as a defender and on the bases. Walker strikes out a lot, as evidenced by a 28% K rate vs. 9% walk rate, but that’s outperforming Goldschmidt’s 101 wRC+ on the season at a total fraction of the cost. Walker might not ever develop into more than an average regular at the 1B position, but for that production Walker will cost a fraction compared to Goldschmidt over the final six years.
Kelly got off to a slow start in Arizona, adjusting to what was at the time a 3-catcher system and learning a new pitching staff. Coming into play May 4th, he hit .182/.211/.309 (30 wRC+) as the team was struggling to get any offense out of the position itself between Kelly and John Ryan Murphy while Alex Avila was on the DL for a quad strain. Things changed for Kelly on May 4th, as he bombed a homer to straightaway center against the Rockies in what turned out to be a dominant 9-2 win over the Dbacks’ division rival. Since then, he’s put up an absurd .333/.430/.657 slash (171 wRC+), which spans over his last 128 trips to the plate, and continuing to grow more and more confident as a hitter as his season line has improved to .282/.362/.540 in 185 PA. Watching him play, Kelly puts up very good ABs almost every time he steps into the box. His OBP numbers are a bit inflated due to the nature of batting 8th in a National League lineup, but even with that in mind there is an OBP and hard hit skill in play with Kelly.
There is a valid concern about possible regression, as Kelly’s wOBA has greatly exceeded his xwOBA to start the season. His xwOBA from May 4th to June 28th is .357, which is 89 points lower than his wOBA over that span according to Statcast. With half of Kelly’s career plate appearances coming over the 2019 season, it’s hard to establish a potential baseline for regression although a .357 wOBA is excellent for a player with his defensive profile if that was the new normal. From the eye test, it looks like Kelly will develop into an above average hitter thanks to solid plate discipline and surprising power. Even if he is lucky on balls in play, Kelly is creating his own luck with a 38.5% hard hit rate (basis being 95+ MPH EV) and an average launch angle of 14º.
Kelly not only has become a very solid hitter, he has also put up excellent numbers behind the plate as well. He’s caught 9 of 25 potential basestealers for a very solid 36% rate as well as rank among the league leaders in pitch framing metrics. I came into the season expecting Kelly to be a solid defender with a below average bat, but he’s completely blown away expectations. He won’t make an All-Star team this year, but he’s definitely put himself on the radar. He ranks 4th amongst NL catchers with 1.7 fWAR (min. 180 PA) and with more playing time and more growth at the plate could establish himself as one of the top catchers in the National League, as the Dbacks will control his rights through the 2024 season. Kelly and Walker by themselves win the trade, but we’re just getting started.
Weaver was on the cusp of a breakout year before a flexor strain and minor UCL damage has shelved him since the end of May. Before that injury, Weaver was looking like a very good #2 starter with ace potential with more development of his breaking pitches. On the season to date, he’s pitched to a 3.03 ERA and 3.07 FIP and was averaging nearly 6 innings a start (62 IP in 11 starts). Weaver is hoping that he can pull a Masahiro Tanaka and successfully rehab the elbow without needing Tommy John surgery and the Dbacks are optimistic he can do that as well. Weaver comes with 4 more seasons of control after the 2019 season and if he can avoid any more catastrophic injuries could settle in as a #2 starter for the rotation behind Zack Greinke and allow the Dbacks to move on from Robbie Ray (I see Ray in a similar light as Goldschmidt last year, sell high and hope for the best).
More advanced metrics paint Weaver more as a #3 type pitcher than a #2 or #1 starter, with an xFIP of 3.78 and SIERA of 3.74. Even if that is Weaver’s true talent level, a controllable middle of the rotation starter is still a solid outcome for the Diamondbacks. Weaver came into Arizona as a fastball/change pitcher with very little development on his curveball and an underutilized cutter. Both breaking pitches have taken a step forward in 2019 while the bread-and-butter FB/CH combo has never been better. Weaver has been able to spot the fastball to the edges of the zone and gotten chases up with a mid 90s heater with above average spin, which plays up due to having that plus change-up that’s about 9-10 MPH slower with good tumble and fade. In 2019, we’ve seen more cutters than curveballs from Weaver with the cutter being the main breaking pitch to RHH.
Young is the forgotten piece in this deal, mostly because of the MLB fallout from the trade being so overwhelmingly positive. After a strong Fall League showing, the Dbacks assigned him to AA to be their primary 2B at that level. It went well for Young, as he hit .260/.363/.453 (140 wRC+) in 263 PA with solid XBH numbers (25) and a HBP-driven OBP (19 HBP on the season). Tim Locastro has made it work in Arizona, putting up average hitting numbers at the plate with elite baserunning. Young’s strong showing got him a promotion to AAA, where he’s biding his time for a call-up either later this year or next year when there is an opportunity for everyday ABs at 2B with Ketel Marte playing CF hopefully full time. He’s behind Ildemaro Vargas and Domingo Leyba on the team’s depth chart simply due to the fact he’s not on a 40-man roster although that will change this offseason. Young has gotten off to a slow start in AAA, but with a sample size of 43 PA I’m not going to put too much thought on that for now.
Competitive Balance B Pick (75th overall)
The Dbacks turned this pick into Arkansas outfielder Dominic Fletcher. Fletcher profiles as a 4th OF type who should see somewhat regular playing time due to above average power and defense tools. The Dbacks gave Fletcher an aggressive assignment out of the gate, sending him to Class A Kane County. He should mostly glide through A ball easily, since he’s played on a top tier Division 1 program. Depending on how the bat develops and if the hit tool becomes average, he may exceed expectations and develop into a starting outfielder.
The development of both Carson Kelly and Luke Weaver have completely swung this trade into the Diamondbacks favor. Kelly looks like an everyday catcher with a strong showing in every facet of the game behind the plate. Before suffering an elbow injury, Weaver was having an All-Star caliber campaign with major improvements in strikeouts, walks, and run prevention skills. The team controls both players through the 2024 season and 2023 seasons, so they should be around when the Diamondbacks hit their next major postseason contention window (next season). In fact, both players are extension candidates for the front office to try to lock up for the next 6+ seasons.
Another domino of the trade has also opened up an opportunity for Christian Walker to get everyday reps at 1B. While there is a major dropoff in production from the Dbacks version of Goldschmidt to Walker, the latter has outperformed the former in the 2019 season alone. Walker is controllable through 2024 and while he has a strikeout problem he offsets it with other useful skills. Walker sits in the 94th percentile in exit velocity and Top 35 in barrel rate per batted ball event and per plate appearance in MLB. Couple that with an athletic profile that should lend himself to be an above average defender and baserunner, I see Walker at worst being an average regular at the position with a bit more upside as he finally gets to work on the kinks in his game without having to worry about getting sent down or dumped from the lineup.
The Minor League half of the trade has shaped up well for the Diamondbacks as well. Andy Young had a successful run at AA coming off a solid Fall League last year. Young had a HBP-driven OBP of .363 that otherwise makes a mediocre 20.2%/6.8% K/BB look better. He’ll need that HBP “skill” to carry over to the majors to be a regular contributor at an average starter level. Dominic Fletcher ended up being the final piece to the trade as the Dbacks used their second Competitive Balance B pick of the night to select him. If either of these two players develop into regulars, that’s just more salt in the wound for the Cardinals and could turn the Paul Goldschmidt trade into the Dbacks version of the Herschel Walker trade in which they trade a star for the means to acquire a bunch of high quality players.