In the past 13 years or so, the Yankees have signed multiple key, World Series-winning Red Sox when they’ve hit free agency. On one hand, there was the Johnny Damon signing. He gave the Yankees four solid seasons of lead-off hitting, culminating in the 2009 season, which ended in a championship.
The other side of the coin is Jacoby Ellsbury. After a good first season, he’s fallen off a cliff, mainly due to injuries. It’s been over a year since he’s last played a game, and for all we know he may have lost an arm.