This Sunday, September 15, is Roberto Clemente Day throughout Major League Baseball. Established in 2002, it’s an annual celebration of the Hall-of-Famer and former Pittsburgh Pirates right fielder’s legacy as a humanitarian.

The true measure of an athlete's impact goes well beyond the playing surface in which they made their name on. On the diamond, Pittsburgh Pirates and Puerto Ri

All of the Pittsburgh Pirates wore No. 21 in celebration of MLB’s Roberto Clemente Day, but rookie Billy Cook paid tribute in ways that captured the essence of the late Hall of Fame right fielder’s style of play.

ON THE COUNTER at the museum, in Pirate black-and-gold, are circular stickers that read "RETIRE 21," a plea for Major League Baseball to do for Clemente what it did for Jackie Robinson and what the National Hockey League has done for Wayne Gretzky: universally retire Clemente's iconic No. 21.

The Kansas City Royals had chances to stamp their six-game road trip with a weekend sweep at PNC Park in Pittsburgh. Instead, the Royals fell short 4-3 Sunday afternoon as the Pirates salvaged a victory on Roberto Clemente Day.

Whether it was cleaning up a local park, helping veterans, or others in need, the Pirates honored their greatest player through service.