The Toronto Blue Jays are wearing the number 21 on their jerseys as part of Major League Baseball’s league‑wide tribute to Hall of Famer Roberto Clemente on Roberto Clemente Day, held each season in mid‑September.

What the number 21 means

  • The 21 honors Roberto Clemente , the legendary Puerto Rican right fielder, Hall of Famer, and humanitarian.
  • MLB created Roberto Clemente Day, when players and staff across the league can wear 21 or a 21 patch to celebrate his legacy on and off the field.
  • Clemente is remembered not just for his statistics (3,000 hits, multiple Gold Gloves, World Series titles) but for his charitable work, which ultimately led to his death in a plane crash during a relief mission in 1972.

Why you’re seeing it on the Blue Jays

  • On Roberto Clemente Day, select Blue Jays players, coaches, and personnel wear jerseys with 21 on the back, sometimes without names, as a direct nod to Clemente’s Pirates jersey.
  • Those who may wear 21 include current Roberto Clemente Award nominees, past winners, players who’ve worn 21 before, and players/coaches of Puerto Rican descent, depending on that year’s MLB guidelines.
  • All MLB clubs also use 21 patches and on‑field logos that day, so seeing “21” all over the field is part of a coordinated league event, not a permanent jersey change.

Quick example from a recent season

  • When the Blue Jays hosted the Rays on Roberto Clemente Day, players like Vladimir Guerrero Jr., Bo Bichette, and manager Charlie Montoyo wore 21 to mark the occasion.
  • Fans noticed that not every player had 21 or a name on the back, which comes down to MLB rules: some are eligible or choose to wear the full 21 jersey, while others just have the commemorative patch.

In short, if you’re watching a Jays game and suddenly everyone seems to be 21 for a night, you’re catching MLB’s annual salute to Roberto Clemente, one of the most respected figures in baseball history.

TL;DR:
The Blue Jays wear 21 on their jerseys on Roberto Clemente Day to honor Roberto Clemente’s legacy as a Hall of Famer and humanitarian, as part of an MLB‑wide tribute.

Information gathered from public forums or data available on the internet and portrayed here.