The crossword solution for the term 'Longtime Red Sox Nickname' is YAZ, which stands for Carl Yastrzemski, a Hall of Fame baseball player who spent his entire 23-year career with the Boston Red Sox. He was an 18-time All-Star and won seven Gold Glove Awards, three batting titles, and the Triple Crown in 1967. He was affectionately known as 'Yaz' by Red Sox fans and is widely considered one of the greatest players in Red Sox history.