Cardinals, Molina homers wearing 21 on Roberto Clemente Day
Pirates will wear Roberto Clemente No. 21
Que Viva Clemente! Roberto Lives On in the Hearts of Latino Major Leaguers – Society for American Baseball Research
Pittsburgh Pirates each don No. 21 to honor Roberto Clemente - ESPN
Some MLB Players Wearing #21, All Wearing 21 Patches Today for Roberto Clemente Day – SportsLogos.Net News
Murphy Hits Homer, Two-Run Single, A's Take 1st From Astros – NBC Bay Area
Report: MLB allowing more players to wear No. 21 on Roberto Clemente Day
All Pirates Wearing #21, Rest of MLB Wears Patches in Honour of Roberto Clemente – SportsLogos.Net News
MLB honors Roberto Clemente in 21st annual event
The Greatest MLB Players of All Time to Wear Each Number from 1 to 50, News, Scores, Highlights, Stats, and Rumors
Carlos Beltran Headlines New Baseball Hall of Fame Candidates - The New York Times
Uniform number (Major League Baseball) - Wikipedia