Why the Cardinals traded for Tyler O’Neill in 2017

Seeking to fill opposing needs, the Cardinals and Mariners swapped intriguing prospects on July 21, 2017, as St. Louis obtained slugging outfielder Tyler O’Neill in exchange for lefthanded pitcher and former first-round pick Marco Gonzalez.

Both teams viewed the trade as an opportunity to trade from a position of depth to fill a need. O’Neill, a 2013 third-round pick out of Maple Ridge, British Columbia, had slugged 56 home runs over the past two seasons in High-A and Double-A. In 396 plate appearances that season with Triple-A Tacoma, O’Neill had hit .244 with 19 homers and 56 RBIs, including a recent, three-week surge in which he hit eight homers, slugged .730, and drove in 17 runs in 16 games. O’Neill’s prodigious power was accompanied by 108 strikeouts in 93 games.

“The one thing that we talk a lot about is finding those bats,” Cardinals president of baseball operations John Mozeliak said. “We definitely feel like our strength is starting pitching in the minor leagues. Not that we’re not proud of our outfield depth, but we do think his offensive profile is unique. Middle-of-the-order potential.”[1]

The son of a former Mr. Canada bodybuilder, MLB.com ranked O’Neill the No. 2 prospect in the Mariners’ system and Baseball America listed him as their No. 35 overall prospect.




“The way you get out of Canada and into the draft is hitting,” O’Neill said. “Of course, whenever you hear the name O’Neill, I know (power) is what people are going to think, but there are more aspects to my game and I think people are going to start to see that.”[2]

According to the Tacoma News Herald, the Mariners viewed O’Neill as expendable following the emergence of rookies Ben Gamel, Mitch Haniger, and Guillermo Heredia.[3]

O’Neill, who needed to be added to the Cardinals’ 40-man roster in the winter, joined a Triple-A Memphis outfield that also featured Harrison Bader. With his addition to Triple-A, he slid ahead of Double-A outfielders Oscar Mercado, Magneuris Sierra, and Randy Arozarena in the depth chart.

“All of that creates more depth for the Cardinals to possibly deal an upper-level outfielder in the coming days,” the St. Louis Post-Dispatch reported. “The Cardinals have been gathering a sense of the interest in players like (Randal) Grichuk and Bader in this market.”[4]




Ultimately, the Cardinals chose not to trade one of their young outfielders ahead of the trade deadline, though they did send Stephen Piscotty to the Athletics that December and dealt Randal Grichuk to the Blue Jays in January 2018.

While the Cardinals sought to add a potential middle-of-the-order bat, the Mariners needed young pitching. Gonzales, who played his college baseball at Gonzaga University in Spokane, Washington, made his major-league debut less than a year after the Cardinals drafted him, going 4-2 with a 4.15 ERA in 10 games (five starts) as a 22-year-old in 2014.

That fall, Gonzales threw three scoreless innings of relief in the NLDS, picking up wins in Game 1 and Game 4 (Clayton Kershaw was the losing pitcher in both games). Gonzales also pitched three innings in the NLCS and took the loss in Game 4.

Following that initial success, however, Gonzales missed most of the 2015 season with a pectoral injury and all of 2016 due to Tommy John surgery. Since returning from the injury in 2017, the 25-year-old Gonzales had posted a 2.78 ERA in 12 starts for Triple-A Memphis.




“Marco is a quality athlete with high character and a strong pitching pedigree who we feel fits our roster well in both the near and long term,” Mariners general manager Jerry Dipoto said. “We find his current performance, preparedness, and proximity to the major leagues to be very appealing traits in a pitcher, particularly a young lefty who is now under club control through the 2023 season.”[5]

Although Gonzales would be out of options after the 2017 season, he would not be eligible for salary arbitration until after 2020.

Dipoto was in attendance when Gonzales made his debut for the Mariners’ Triple-A Tacoma squad, allowing three runs and striking out five over six innings.

“As we were told, he’s a thrower with a plus changeup, and that’s what he did,” Tacoma manager Pat Listach said. “That’s the first time I’ve ever seen him and he came as advertised.”[6]




“Everything has been really, really smooth,” Gonzales said. “I have been really blessed and thankful that I have worked with some great people with the Cardinals that have enabled me to come back strong and enabled me to get back on the field without pain. This year has been a blessing just because of that.”[7]

Back in St. Louis, Post-Dispatch columnist Jeff Gordon approved of the trade.

“Gonzales was caught in a logjam here, even with (Lance) Lynn on the trade block,” he wrote. “(Luke) Weaver passed him on the organizational ladder. So did (Jack) Flaherty. (Dakota) Hudson is developing quickly and Alex Reyes is on schedule to return next season after recovering from Tommy John surgery. The Cardinals have a lot of young pitchers and could leverage that to gain substantially more power.”[8]

Unfortunately, the Cardinals’ next trade to turn young pitching depth into offensive firepower took the form of a December 14, 2017, deal that sent Sandy Alcantara, Daniel Castano, Zac Gallen, and Sierra to the Marlins for Marcell Ozuna.




The O’Neill-for-Gonzales trade, however, ultimately proved relatively successful for both sides. O’Neill made his big-league debut for the Cardinals as a 23-year-old in 2018, and provided a glimpse of his power potential, slugging nine home runs in just 61 games.

He made the Cardinals’ opening-day roster in 2019, but injuries and inconsistent performance limited him to just 60 major-league games. In 2020, O’Neill won his first Gold Glove Award in left field, and in 2021 he enjoyed the best season of his career to date, batting .286 with 34 homers, 80 RBIs, and 15 stolen bases. He placed eighth in that year’s National League MVP balloting and was recognized with his second Gold Glove.

In 2022 and 2023, however, O’Neill once again was plagued by injuries. In 2022, he hit just .228 with 14 homers and 58 RBIs in 96 games. The following year, he appeared in just 72 games, batting .231 with nine homers and 21 RBIs. On December 8, 2023, the Cardinals traded him to the Red Sox for pitchers Nick Robertson and Victor Santos.




Though O’Neill was unable to sustain his 2021 success, that season alone represented a good return for Gonzales, whose lack of options following the 2017 season meant the Cardinals would be unable to send him to the minors without risking another team claiming him.

Gonzales appeared in just two games for Triple-A Tacoma following the trade before the Mariners called him up. In 10 big-league appearances that season, he went 1-1 with a 5.40 ERA over 36 2/3 innings. In 2018, he went 13-9 with a 4.00 ERA and won a career-high 16 games the following year with a 3.99 ERA.

Across seven seasons with the Mariners, Gonzales went 61-47 with a 4.08 ERA. On December 3, 2023, the Mariners traded Gonzales, Jarred Kelenic, and Evan White to the Braves for Jackson Kowar and Cole Phillips. Two days later, the Braves flipped Gonzales and cash to the Pirates for a player to be named later.


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[1] Derrick Goold, “Cards deal Gonzales for outfielder,” St. Louis Post-Dispatch, July 22, 2017.

[2] Derrick Goold, “O’Neill makes Memphis debut,” St. Louis Post-Dispatch, July 24, 2017.

[3] Bob Dutton, “Mariners acquire lefty from Cardinals,” Tacoma News Tribune, July 22, 2017.

[4] Derrick Goold, “Cards deal Gonzales for outfielder,” St. Louis Post-Dispatch, July 22, 2017.

[5] Bob Dutton, “Mariners acquire lefty from Cardinals,” Tacoma News Tribune, July 22, 2017.

[6] Terrence Holmes, “Mariners GM sees new asset shine in debut,” Tacoma News Tribune, July 25, 2017.

[7] Terrence Holmes, “Mariners GM sees new asset shine in debut,” Tacoma News Tribune, July 25, 2017.

[8] Jeff Gordon, “Cards’ retooling shouldn’t be limited to the trade deadline,” St. Louis Post-Dispatch, July 25, 2017.

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