Major League Baseball typically sees more than 200 trades each year, and some of these transactions can have lingering consequences for years. This analysis examines several trades executed between January 1, 2017, and December 31, 2023, that have proven to be particularly regretful for the teams involved. Each of these transactions resulted in at least one player having the potential to remain under the team's control through the 2025 season. Notably, trades like Baltimore's exchange of Manny Machado in 2018, Boston's deal involving Mookie Betts in 2020, and Miami's departure of Christian Yelich in 2018 do not qualify because those players were set to become free agents soon after the trades. However, the transfers of Dylan Cease and Eloy Jiménez from the Cubs to the White Sox in 2017 and Adolis García from St. Louis to Texas in 2019 are more significant, as those players have not yet reached free agency, showcasing the enduring impact of these trades.

The first trade under scrutiny is the exchange between the Chicago Cubs and the Chicago White Sox on July 13, 2017, where the Cubs sent Dylan Cease, Eloy Jiménez, Bryant Flete, and Matt Rose in return for José Quintana. At that time, the Cubs viewed Quintana as a solid investment, expecting 3.5 years of top-tier performance at a manageable cost. With a five-year contract extension worth $26.5 million already in place, Quintana had proved to be a reliable pitcher from 2012 to 2016, rated as one of the top pitchers in baseball. However, Quintana's performance fell short of expectations; his best season in Chicago saw him record just 1.5 bWAR. In stark contrast, Cease emerged as a formidable pitcher for the White Sox, nearly winning the AL Cy Young Award in 2022, while Jiménez also showed promise, earning accolades in his early years. The Cubs are likely left reflecting on what could have been with both players.

Another transaction that continues to haunt its originating team occurred on December 14, 2017, when the St. Louis Cardinals traded Sandy Alcántara, Zac Gallen, Daniel Castano, and Magneuris Sierra to the Miami Marlins in exchange for outfielder Marcell Ozuna. Despite Ozuna delivering solid performances during his tenure with the Cardinals, he lacked the star power exhibited by Alcántara and Gallen, who have since developed into two of the premier pitchers in baseball. Alcántara claimed the 2022 Cy Young Award, proving to be an invaluable asset for the Marlins, while Gallen has found comparable success. If the Cardinals had retained both players, they would have been positioned to significantly bolster their roster, rather than navigate a challenging rebuilding phase just as Gallen approaches free agency.

The trade that sent Chris Archer from the Tampa Bay Rays to the Pittsburgh Pirates on July 31, 2018, serves as another example of a regrettable decision. In exchange for Archer, the Rays received Tyler Glasnow, Austin Meadows, and Shane Baz. Archer had previously established himself as a promising pitcher, but he struggled following this trade, culminating in a lackluster tenure for the Pirates. In comparison, Glasnow and Meadows became crucial players for Tampa Bay, contributing significantly to the team's success and showcasing the inadequate return the Pirates received in the deal.

A particularly notable regrettable move by the Cardinals was their December 21, 2019, trade of Adolis García to the Texas Rangers for cash considerations. Initially viewed as a minor transaction without much consequence, Garcia has since developed into a two-time All-Star and Gold Glove winner, solidifying his position as an important player in the league. Meanwhile, the Cardinals have witnessed a consistent struggle to find stability in right field, resulting in a continuous turnover that has not yielded satisfactory results. García's emergence stands in stark contrast to the mediocrity the Cardinals have faced in that position, emphasizing the long-term consequences of this trade.

Moreover, the trade executed by the Colorado Rockies on February 2, 2021, which saw Nolan Arenado and $51 million move to the St. Louis Cardinals in exchange for several minor league players, remains a point of contention. While the Rockies anticipated Arenado's exit via free agency, the return they received was minimal, with only one of the players proving somewhat viable at the major league level. This trade not only lowered the Rockies' standings in the division but also intensified the risk that they would lose one of the game's premier talents without receiving substantial value in return.

On July 30, 2021, the New York Mets traded Pete Crow-Armstrong to the Chicago Cubs in exchange for Javier Báez and Trevor Williams. This deal was intended to improve the Mets' chances down the stretch during a critical season. However, while Báez and Williams contributed to the team, the Mets stumbled, finishing the season without reaching the playoffs. In the aftermath, Crow-Armstrong has ascended to become one of the top prospects in baseball within the Cubs' system, leaving the Mets to ponder what might have been had they retained him instead.

A trade that recently drew scrutiny involved the Minnesota Twins acquiring Tyler Mahle from the Cincinnati Reds on August 2, 2022. At the time, the swap appeared advantageous for Minnesota, offering depth to their rotation without sacrificing top-tier prospects. However, Mahle's unexpected shoulder injury limited his contributions significantly, and he went on to require Tommy John surgery, leaving the Twins questioning the decision. Meanwhile, Spencer Steer, one of the prospects sent to Cincinnati, has thrived in the MLB, further compounding the situation for the Twins.

The Los Angeles Angels made a headline-grabbing move on July 26, 2023, when they traded prospects Ky Bush and Edgar Quero to the Chicago White Sox for pitchers Lucas Giolito and Reynaldo López. Seeking to rejuvenate their chances within Shohei Ohtani's likely final season with the team, the Angels made this trade with high expectations. Unfortunately, Giolito's performance was disappointing, posting a 6.89 ERA in his outings, leading to his placement on waivers. This transaction ultimately left the Angels without a considerable return on their investment, further compounding their struggles as they pursued a postseason berth.

Finally, the Boston Red Sox's trade of Chris Sale to the Atlanta Braves on December 30, 2023, has raised eyebrows among analysts. Initially perceived as a way to shed Sale's salary, the deal shockingly involved sending Atlanta over $17 million while acquiring middle infield prospect Vaughn Grissom. With Sale going on to win the NL Cy Young Award in 2024 and Grissom failing to make an impact for the Red Sox, Boston may end up regretting the trade for years to come. Grissom's future with the team appears uncertain due to other infield prospects competing for similar positions, potentially cementing this trade as one of the most lopsided deals of the past decade.