Yankees pitcher Mike Mussina officially retired on Thursday just weeks after recording his first 20-win season, and New York captain Derek Jeter weighed in on his decision. "It was a great pleasure playing against?and even more so?with Mike Mussina since I entered the league in 1995. He was a true professional both on and off the field," Jeter said in a statement. "Moose's accomplishments in the game over the last 18 years represent a Hall of Fame player."