Mookie Betts is wearing number 21 as a tribute to Roberto Clemente on Roberto Clemente Day, and because he has been selected as a nominee for the Roberto Clemente Award, which recognizes players for their humanitarian and community work off the field.

Quick Scoop: Why Is Mookie Wearing 21?

On specific September dates, MLB celebrates Roberto Clemente Day across the league. On that day, certain players are allowed to wear Clemente’s iconic number 21 instead of their usual jersey number.

For Mookie Betts and a few others, that’s exactly what’s happening.

  • MLB designates September 15 as Roberto Clemente Day each season.
  • Select players, including Roberto Clemente Award nominees and past winners, are allowed to wear number 21 in Clemente’s honor.
  • Mookie Betts wore 21 for the Dodgers in games against teams like the Braves and Phillies specifically because he was a Roberto Clemente Award nominee.
  • Puerto Rican players (Clemente was Puerto Rican) are also allowed to wear 21 in tribute, even beyond just one player per team.

So if you see Mookie in 21, it’s not a number change or a new permanent jersey—it’s a special one-day tribute tied to Clemente’s legacy and MLB’s humanitarian award.

A Bit More Context

Roberto Clemente is one of baseball’s most revered figures, not only for his Hall of Fame career with the Pittsburgh Pirates but for his humanitarian work off the field. After his death in a plane crash while delivering aid to earthquake victims in Nicaragua in 1972, MLB renamed its top community-service honor the Roberto Clemente Award.

  • The award was originally called the Commissioner’s Award when created in 1971.
  • It was renamed in 1973 to honor Clemente’s memory and his commitment to helping others.
  • Each team nominates one player every year; those nominees (and past winners) can wear 21 on Roberto Clemente Day as part of league-wide celebrations.

In recent seasons, Mookie Betts has been one of those nominees, which is why you’ve seen him switch from his usual number 50 to 21 for that game.

Why is “Why is Mookie wearing 21” trending?

The phrase “why is mookie wearing 21” spikes every time Clemente Day games are on TV, especially when the Dodgers are in a marquee matchup. Many casual viewers don’t know about the one-day jersey exception and assume it’s a random number change, which fuels quick forum threads, social posts, and search trends around that question.

Fans on forums and social media often post real-time reactions like:
“Did Mookie switch numbers?” or “Why is everyone wearing 21 today?” during those broadcasts.

In short: it’s a recurring mini-mystery for anyone not familiar with Clemente Day—but the answer is a respectful, league-wide tribute to one of baseball’s greatest humanitarian figures.

TL;DR: Mookie Betts wears 21 on Roberto Clemente Day because he’s a Roberto Clemente Award nominee, and MLB allows those players (plus certain others) to honor Clemente by wearing his number for that game.

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