Jon Lester
The Jon Lester trade had a big impact on the Red Sox almost a decade later and also presaged what would eventually happen to Mookie Betts, but we’ll get to that in a bit. The big lefty came up through the Red Sox system and made his major league debut in 2006. He’d go on to be a durable member of the Sox rotation until 2014.
Lester’s story was extra special because of what he overcame. In 2006 he missed the last month and a half of the season due to being diagnosed with lymphoma. After undergoing treatment and successfully beating it into remission, Lester returned to the Red Sox in mid-2007. He ended up being a key contributor to the 2007 World Series champs and even won the clinching game of the series, which was also his first career postseason start.
Lester would go on to throw a no-hitter in 2008 and help the Red Sox win another World Series in 2013. However, when his free agency was approaching the Red Sox lowballed him with contract offers. Lester said in the press he’d be willing to take a hometown discount, but the Red Sox front office took the “discount” part of that statement too much to heart.
Instead, they traded him at the 2014 deadline to Oakland for Yoenis Cespedes. Lester finished the season in Oakland, rebuffed the Red Sox contract offer in free agency, and signed with the Chicago Cubs where he won another World Series in 2016. Cespedes hit fairly well in Boston, putting up a .259 average along with 5 home runs and 33 RBI. However, the Red Sox ended up trading him after the season to Detroit for Rick Porcello.
Lester in his Red Sox career went 110-54 with a 3.75 ERA and 1386 strikeouts. Losing Lester and the fan backlash around it led to the Red Sox outbidding themselves to sign David Price in 2015, a deal that would have a ripple effect a few years later.