On Tuesday night, the Boston Red Sox ended months of low-level disbelief and bemusement—and incited several news cycles of intense disbelief and bemusement—by following through on their long-rumored intention to trade right fielder Mookie Betts. Boston reportedly sent Betts, along with pitcher David Price and cash, to the Los Angeles Dodgers in a three-team trade, netting 23-year-old Dodgers outfielder Alex Verdugo and 21-year-old Minnesota Twins pitcher Brusdar Graterol in return. (The Dodgers sent pitcher Kenta Maeda to the Twins to seal the deal.)

A deal of this magnitude demands multiple angles of inquiry: what it means for the Dodgers from a competitive standpoint; what it means for the Red Sox from a financial and competitive standpoint; what it tells us about baseball’s economics at large; and, less pressingly, what it means for Minnesota. I’m not going to tackle all of those angles here. I’m here to express something simple: the stupendous improbability that a player like Mookie was moved at all. To put it plainly: This swap is unprecedented. No player boasting Betts’s combination of excellence and youth has ever been traded before.

When ESPN’s Jesse Rogers surveyed 15 baseball insiders in late November about which of the three 20-something superstars rumored to be on the block—Betts, Francisco Lindor, and Kris Bryant—was most likely to be traded, zero picked Betts. That’s partly because the Red Sox are a big-market, deep-pocket franchise with a title less than 2 years old and a competitive roster, which makes them precisely the last type of team that typically considers off-loading a widely beloved player who made them much better (as noted, a subject for a separate article). But it’s also partly because Betts isn’t just any perennial all-star. He’s baseball’s second-best player, and he’s still in his prime. That’s not the type of player any team tends to trade.

Betts, a career .301/.374/.519 hitter, is coming off a season in which he hit .295/.391/.524, with 29 homers and his usual stellar defense and baserunning. He won a Gold Glove and a Silver Slugger Award and finished eighth in American League MVP voting, and his 6.8 Baseball-Reference WAR ranked fourth among AL position players.

That was a down year.

The year before that, Betts mashed to the tune of a .346/.438/.640 slash line with 32 homers in 136 games, in a year with a less lively ball relative to 2019. He won the AL MVP award, garnering 28 of the 30 first-place votes, and he generated 10.9 Baseball-Reference WAR, the highest single-season mark posted by any position player since Barry Bonds in 2002. (Only 20 position-player seasons have ever been better.) Mookie’s 2015-17 seasons were stellar, too: He came close to winning an MVP award in 2016, finishing second behind Mike Trout, and in each of the past four years, he’s made the All-Star team, won a Gold Glove, and finished no lower than eighth in MVP voting.

By B-Ref WAR, Mookie has been the most valuable player in baseball, besides Trout, in the past two seasons. He’s also been baseball’s best non-Trout player in the past three, four, five, and six seasons—and six seasons ago, in 2014, Betts was a rookie who didn’t make his major league debut until late June.

In the past two seasons, Mookie has amassed 17.7 B-Ref WAR. No player 28 or younger who has ever been traded accrued that much WAR in the two full seasons preceding the swap. The list below presents the top 20, with Mookie outpacing all previous trade acquisitions (including two other Red Sox outfielders who won MVP awards in earlier years, Tris Speaker and Fred Lynn). Keep in mind that Mookie’s 2016-17 seasons were worth a combined 16.2 WAR, so it’s not as if we’re citing a two-season sample to obscure a spottier long-term track record. Betts has been great for several seasons, which is particularly impressive in light of his age.

Highest Combined WAR Totals in Two Seasons Preceding a Trade, Players 28 or Younger Player Year 1 Y1 WAR Y2 WAR Total WAR From To Age Traded Date Player Year 1 Y1 WAR Y2 WAR Total WAR From To Age Traded Date Mookie Betts 2019 6.8 10.9 17.7 BOS LAD 27.3 Offseason 2/4/2020 Jimmie Foxx 1935 8.4 9.0 17.4 PHA BOS 28.1 Offseason 12/10/1935 Alex Rodriguez 2003 8.4 8.8 17.2 TEX NYY 28.6 Offseason 2/16/2004 Tris Speaker 1915 7.1 9.9 17.0 BOS CLE 28.0 Offseason 4/9/1916 Josh Donaldson 2014 7.5 7.7 15.2 OAK TOR 28.9 Offseason 11/28/2014 Ned Garver 1951 6.6 8.0 14.6 SLB DET 26.6 Midseason 8/14/1952 Zack Greinke 2010 3.4 10.4 13.8 KCR MIL 27.2 Offseason 12/19/2010 Bert Blyleven 1975 6.0 7.8 13.8 MIN TEX 25.2 Midseason 6/1/1976 Fred Lynn 1980 4.7 8.8 13.5 BOS CAL 28.9 Offseason 1/23/1981 Jim Abbott 1992 5.7 7.6 13.3 CAL NYY 25.2 Offseason 2/6/1992 Ubaldo Jimenez 2010 7.3 5.9 13.2 COL CLE 27.5 Midseason 7/30/2011 Rickey Henderson 1984 6.0 6.9 12.9 OAK NYY 25.9 Offseason 12/5/1984 Johnny Mize 1941 5.4 7.4 12.8 STL NYG 28.9 Offseason 12/11/1941 Johan Santana 2007 5.2 7.6 12.8 MIN NYM 28.9 Offseason 2/2/2008 Pedro Martínez 1997 8.8 3.8 12.6 MON BOS 26.1 Offseason 11/18/1997 Dizzy Dean 1937 4.9 7.6 12.4 STL CHC 28.2 Offseason 4/16/1938 Graig Nettles 1972 4.8 7.5 12.3 CLE NYY 28.3 Offseason 11/27/1972 Rusty Staub 1971 6.0 6.3 12.3 MON NYM 28 Offseason 4/5/1972 Bert Blyleven 1977 5.8 6.5 12.3 TEX PIT 26.7 Offseason 12/8/1977 Joe Jackson 1914 4.6 7.6 12.3 CLE CHW 28.1 Midseason 8/21/1915

What if we open this up to all traded players? Here’s the top 20 with age restrictions removed:

Highest Combined WAR Totals in Two Seasons Preceding a Trade, Players of All Ages Player Year 1 Y1 WAR Y2 WAR Total WAR From To Age Traded Date Player Year 1 Y1 WAR Y2 WAR Total WAR From To Age Traded Date Pete Alexander 1917 9.8 12.0 21.7 PHI CHC 30.8 Offseason 12/11/1917 Roger Clemens 1998 8.1 12.1 20.2 TOR NYY 36.5 Offseason 2/18/1999 Rogers Hornsby 1928 8.8 10.1 18.9 BSN CHC 32.5 Offseason 11/7/1928 Wes Ferrell 1936 7.8 10.6 18.4 BOS WAS 29.4 Midseason 6/11/1937 Mookie Betts 2019 6.8 10.9 17.7 BOS LAD 27.3 Offseason 2/4/2020 Jimmie Foxx 1935 8.4 9.0 17.4 PHA BOS 28.1 Offseason 12/10/1935 Alex Rodriguez 2003 8.4 8.8 17.2 TEX NYY 28.6 Offseason 2/16/2004 Cy Young 1908 9.6 7.6 17.2 BOS CLE 41.9 Offseason 2/16/1909 Tris Speaker 1915 7.1 9.9 17.0 BOS CLE 28.0 Offseason 4/9/1916 Jim Bunning 1967 8.0 9.0 16.9 PHI PIT 36.1 Offseason 12/15/1967 Lefty Grove 1933 7.4 9.3 16.6 PHA BOS 33.8 Offseason 12/12/1933 Gaylord Perry 1974 8.5 7.8 16.3 CLE TEX 36.7 Midseason 6/13/1975 Frank Viola 1988 7.7 8.1 15.8 MIN NYM 29.3 Midseason 7/31/1989 Curt Davis 1935 7.0 8.5 15.5 PHI CHC 32.7 Midseason 5/21/1936 Chuck Knoblauch 1997 6.8 8.6 15.4 MIN NYY 29.6 Offseason 2/6/1998 Josh Donaldson 2014 7.5 7.7 15.2 OAK TOR 28.9 Offseason 11/28/2014 Hughie Jennings 1898 7.5 7.3 14.8 BRO BAL 30.3 Midseason 8/3/1899 Rod Carew 1978 5.0 9.7 14.7 MIN CAL 33.3 Offseason 2/3/1979 Jim Kaat 1975 7.7 7.0 14.7 CHW PHI 37.1 Offseason 12/10/1975 Rogers Hornsby 1926 4.4 10.2 14.6 STL NYG 30.6 Offseason 12/20/1926

Even when we include acquisitions of all ages, only four players place ahead of Betts. Only one player changed teams within the past 80 years (Roger Clemens, who was dealt in early 1999 at 36 years old by a Blue Jays franchise that hadn’t made the playoffs for five seasons and wouldn’t make the playoffs for 17 more). If we lump in players who were “purchased,” not traded, our search turns up three more post-19th-century names in the neighborhood of Betts (all Hall of Famers).

Connie Mack’s Philadelphia Athletics, which engaged in a post-1914 fire sale that would have made Jeffrey Loria blush, sold Eddie Collins (of “$100,000 infield” fame) to the White Sox at the Betts-ian age of 27.6, coming off a two-season span in which Collins managed a Betts-ian WAR total of 18.0. Years later, Mack’s A’s sold another star to the White Sox, Al Simmons (15.2 WAR from 1930-31). And then there’s the purchase that looms largest in the annals of infamous Boston transactions: On the day after Christmas in 1919, Babe Ruth was sold to the Yankees with a two-season total of 16.9 WAR, which was just a taste of even loftier WAR totals to come.

A few players Betts’s age or younger have been traded coming off a single season with a WAR as high as Betts’s 2019 total: Pedro Martínez was traded to Boston in November 1997 (26.1 years old, 8.8 WAR in ’97); Mike Hampton moved to the Mets in December 1999 (27.3 years old, 7.8 WAR in ’99), and Dave Roberts—the pitcher, not Mookie’s new manager—went to the Astros in December 1971 (27.2 years old, 7.8 WAR in ’71). But Mookie’s age and accomplishments in a two-season span set him apart from any other player traded in almost 150 years of major league history. Add in all the other factors that made a trade less likely in this specific case—that Mookie is a model citizen; that he’s a fan favorite; that he was drafted and developed by the Red Sox; that he recently won a World Series in Boston; that the Red Sox are the third-most-valuable MLB franchise; and that the Fenway Sports Group, which owns the Red Sox, is the world’s third-most-valuable sports conglomerate—and it’s mind-boggling that Mookie was moved.

The Red Sox can try to mollify their Betts-bereaved fan base by citing the star’s escalating salary: He’s due to earn $27 million this season, a record for a player in his final year of arbitration eligibility. They can note that Betts is 10 months away from free agency, that he reportedly rejected modest extension offers and expressed some willingness to test the open market, and that if Boston was outbid for his services next offseason, the Sox would have had only a draft pick to show for the loss of their star. They can spin their desire to plunge their payroll below the competitive balance tax threshold as a means of boosting spending in seasons to come. They can point out that the Sox missed the playoffs in 2019 even with Betts, and that the Yankees and Rays are still strong. They can draw attention to the considerable talents of Verdugo and Graterol and tally the two players’ remaining team-control years.

But Betts was already a top-10 position player in Red Sox franchise history, and he was just getting started. Verdugo and Graterol are promising players, and the Sox may eventually put their savings on Betts and Price toward signing some other stud. To heal this wound, they’ll have to, because Betts is the rare talent who takes two or three stars to replace, and like Trout, he’s virtually impossible to overpay. Carl Sagan said that extraordinary claims require extraordinary evidence. The corollary in sports says that extraordinary trades require extraordinary justifications. In other words, the Red Sox have some explaining to do. And the already outstanding Dodgers, who’ve largely kept their prospect powder dry and resisted making splashy signings and trades during Andrew Friedman’s tenure, can brag about treating their fans to a future Hall of Famer whom history says should have been off limits.

Thanks to Dan Hirsch of Baseball-Reference for research assistance.