Why some players have No. 21 on back of their baseball caps
To Pirates catcher Michael Perez, wearing No. 21 'very special
Nats DH Cruz, other Clemente Award winners wear '21' on caps
MLB expands list of who can wear No. 21 to honor Roberto Clemente on Sept. 15 - ESPN
Cardinals notebook: Besides Lars Nootbaar, four others wear No. 21 in Clemente's honor
Padres should retire Caminiti's #21 before it's too late
Spartans Tangle With Wolverines In B1G Weekend Series - Michigan State University Athletics
Roberto Clemente: Cincinnati Reds' José De León wants MLB to retire 21
ROBERTO CLEMENTE - PITTSBURGH PIRATES - #21 SMALL PATCH IN PACKAGE UNSOLD - RARE
It's time for Roberto Clemente's No. 21 to be retired across baseball - Bucs Dugout
Wearing Roberto Clemente's No. 21 an honor for Francisco Lindor, Sandy Alomar Jr. and all Puerto Rican-born Cleveland Indians