There have only been a handful of players who have been a part of World Championships with both the Red Sox and the Yankees. Obviously, the major reason behind this is the fact that Boston went so long without a World Championship. That, and to a lesser extent, the fact that it took quite awhile before the Yankees won their first World Championship. Boston was a bit of a dynasty in the 1910's, winning four World Championships between 1912 and 1918. They also won in 1903. But after 1918, they would not win another one until 2004. The Yankees meanwhile won their first World Championship in 1923 and went on to win significantly more than any other team.
The list of players to win World Championships with both teams is small, and dominated by players from the late 1910's/early 1920's. I am only counting players that actually played in the World Series with both teams, so Herb Pennock, Waite Hoyt, and Ramiro Mendoza, for example, will not be counted.
BULLET JOE BUSH
Owner of an awesome nickname, Bullet Joe Bush was also a pretty decent pitcher who started out with the Philadelphia Athletics where he won a World Series in 1913. He was acquired by Boston in the same deal that brought Wally Schang and turned in a 15-15 season with a 2.11 ERA and then took a loss in the 1918 World Series. Bush then pitched two games for the Yankees in the 1923 World Series.
Next to David Ortiz, Damon is probably the most iconic player from the 2004 World Champion Red Sox. Damon was one of the original "Idiots", the pet name for the lovable World Champs. Damon infamously left the Red Sox as a free agent after the 2005 season to join the Yankees where he had to cut his long hair and shave his beard. He had some big moments with the Yankees on their 2009 World Championship run.
The most obscure player on this list, Hinske is mostly known for winning the 2002 AL Rookie of the Year award with the Blue Jays. This post started as a way to show off this card which I just received. Hinske became a role player after a few years and picked up one at-bat for each team in the World Series. He was with the Red Sox in 2007 and the Yankees in 2009. He also played in the World Series for the Rays in 2008, making three World Series appearances in three consecutive years, with three different teams.
SAD SAM JONES
Another pitcher with a great nickname, Jones was a very good pitcher with the late 1910's/early 1920's Red Sox and even won 23 games in 1921 for Boston. He was 16-5 with a 2.25 ERA for the 1918 World Champs and took a loss from the Cubs in the World Series. He played in three World Series with the Yankees, and was on the 1923 championship team.
The Sultan of Swat needs no introduction. He was on the Red Sox team in 1915, but because that team had such an amazing staff, neither him nor Smoky Joe Wood was even needed in the World Series, though he did appear in a pinch-hitting role. He did pitch in the 1916 and 1918 World Series with the Red Sox and even set a record with 29 1/3 consecutive scoreless innings in the World Series. Ruth was a four-time World Champion with the Yankees in 1923, 1927, 1928, and 1932, the last of which was the setting for his famous alleged "Called Shot".
Schang was a versatile player who spent quite a bit of time behind the plate. He was something of an underrated player and should be in the Hall of Fame instead of Ray Schalk. Schang had some good years with both teams and appeared with the Red Sox in the 1918 World Series and the Yankees with the championship team in 1923. He also won a World Championship with the Philadelphia Athletics.
A classic good-fielding, non-hitting middle infielder, Scott started out his career as the starting shortstop for three World Championship Red Sox teams (1915, 1916, 1918). He was traded to the Yankees after the 1921 season and played on the 1923 World Champion Yankees team. Scott is mostly well-known for his consecutive games streak which reached 1,307 games which was the record before Lou Gehrig broke it and is still third all-time.