New York Yankees history: Paul O'Neill's number 21 must be retired
Every MLB team's retired numbers – NBC Sports Philadelphia
NY Yankees royalty honored as Paul O'Neill's No. 21 is retired
Paul O'Neill Number Retirement Ceremony
Going where everybody knows his name: Paul O'Neill joins “Cheers” reboot
Paul O'Neill Book Excerpt: A Memorable Chat With Ted Williams - The New York Times
Paul O'Neill on No. 21 retirement Yankees
Paul O'Neill will finally have number retired by Yankees
Frustrated Cole, Boone pound away, shaky Yanks fall to Jays
Yankees to retire Paul O'Neill's No. 21 jersey on Aug. 21
Monument Park (Yankee Stadium) - Wikipedia
Predicting the Next Retired Number for Every Team - The Crawfish Boxes
Paul O'Neill recalls final Yankees game, how close he came to return in new book