It's a fact of the game that players will move from team to team over the course of a major league career. However, it always hurts a little extra when a player on the Red Sox crosses over to join the Yankees.
The Red Sox and Yankees have been rivals since baseball evolved, and fans of one team have never liked players of the other. "Hate" is a strong word, but it's not out of the question for fans to sometimes hate a former Sox player now donning the pinstripes.
Roger Clemens was in the news recently for his perjury trial, but Sox fans know him as one of the best pitchers in baseball. He began his career with the Sox in 1984 and stayed with the club all the way to 1996. After the Sox, Clemens had a two-year stint with the Blue Jays before heading to New York. The Rocket was heralded as one of the best Red Sox pitchers of all-time, so it hurt to see him win a Cy Young award and two World Series, which he couldn't do for the starving Red Sox faithful.
Johnny Damon, on the other hand, led one of the most popular Red Sox teams ever to a World Series in 2004. Two years later, he left Boston in dramatic fashion and joined the Yankees. Damon went from being the guy everyone loved and that looked like Jesus, to a clean-shaven Yankee that everyone hated. He played out his four-year contract with the Yankees and helped deliver them a World Series in 2009.
Another face that Red Sox fans had to suffer through seeing win a ring in New York belonged to Wade Boggs. He played 11 seasons with the Red Sox and looked like a guy who would be a Red Sox for life. But when his contract came up after the 1993 season, he pursued other options. After much deliberation he choose the rival Yankees, where he seemed to revive his career.
Lastly, Babe Ruth used to be a member of the Boston organization, but was sold to the New York Yankees, creating the so-called "Curse of the Bambino." Ruth ended up being one of the best players of all time, and had immense power that no one else in his era could match. While it's true that Ruth didn't choose to leave the Red Sox by choice, he did leave his mark on New England — and the Red Sox — forever.