According to Evan Drellich of the Boston Herald, right-handed starter Anderson Espinoza is going back to the Padres in the deal.
Pomeranz, 27, is enjoying the best season of his career. In 102 innings over 17 starts, he has gone 8-7 with a 2.47 ERA and a 115 to 41 strikeout-to-walk ratio. Advanced stats such as FIP (3.18) and xFIP (3.66) also view Pomeranz favorably.
This season, Pomeranz has already been worth 2.5 Wins Above Replacement (fWAR), which ranks him ninth among National League starting pitchers. He was just named to his first All-Star Game.
Over his career, Pomeranz has struggled to get lots of playing time. Even still, however, he carries a strong 3.66 ERA in parts of six seasons with the Rockies, Athletics and Padres. With just three years and thirteen days of service time coming into the season, he will also remain a cheap option for Boston.
The Padres acquired Pomeranz from the Athletics during the offseason, and they avoided arbitration with a one-year, $1.35 million deal. He is not a free agent until after the 2018 season.
In a market where starting pitching comes few and far between, Pomeranz is a big get for the Red Sox. Their starting pitching has been among the worst in the American League, ranking 9th in Wins Above Replacement and posting the seventh-highest ERA.
Boston has shown the ability to contend thus far, as they are currently tied for a Wild Card spot in the AL. At 49-38, they are just two games out of the division-leading Orioles.
Even though Pomeranz fills a large need in Boston, he does come at an expensive price. Boston dealt 18-year-old Anderson Espinoza to get him.
Espinoza is currently pitching at Class A Greenville, where he is 5-8 with a 4.38 ERA and a 72 to 27 strikeout-to-walk ratio in 76 innings pitched. While the results might not look pretty, he is definitely a good return for San Diego, ranking fourth on the Red Sox's top prospect list (via MLB.com) and 39th overall prior to the season.
With the trade of Pomeranz, the Padres may be more inclined to fully sell off the rest of their roster. This could include dealing first baseman Wil Myers, catcher Derek Norris or outfielders Matt Kemp and Melvin Upton Jr.