Puerto Rican players follow Pirates' push to wear No. 21, celebrate Roberto Clemente
Roberto Clemente in Retrospect - Pittsburgh Quarterly
Roberto Clemente's No. 21 is 'retired in our hearts' but not on most MLB rosters - The Athletic
MLB celebrates Roberto Clemente Day
Pirates will honor Roberto Clemente by wearing his No. 21 on their jerseys - ESPN
Roberto Clemente's death 50 years ago forever changed his son, a former Phillies minor leaguer
Campaign To Retire Roberto Clemente's No. 21 Throughout MLB Gains Traction
Reds' Michael Lorenzen changed his number to 21 to honor Roberto Clemente
Living out the legacy: Curve retire No. 21 as reminder of Clemente's greatness