Why are MLB players wearing 21 on their sleeve? - Quora
Roberto Clemente: Cincinnati Reds' José De León wants MLB to retire 21
All Pirates Wearing #21, Rest of MLB Wears Patches in Honour of Roberto Clemente – SportsLogos.Net News
Jackie Robinson Day, when MLB players can wear No. 42
Baseball Joins Other Sports in Flexing Its Activist Muscles - The New York Times
For the 'Great One': PittsburghPirates, Major League Baseball honor Roberto Clemente
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Opening Day in MLB: New No. 21 patches, NL DHs and Guardians
Baseball United announces historic player draft for new Dubai-based professional league
Baseball Celebrates Clemente with “21” Patches; Pirates and Award Winners All Wearing #21 – SportsLogos.Net News
Dodgers News: Kiké Hernandez, Edwin Rios Honored To Wear No. 21 On Roberto Clemente Day
New generation takes over Coors Field All-Star Game at time when baseball needs it most: What a bonanza for the game