Hakim Warrick wears #21 for the Memphis Grizzlies.
LaDanian Tomlinson wears number 21. He is on the San Diego Charges.
Roberto Clemente- Outfielder Pittsburgh Pirates
Sammy Sosa- Outfielder Chicacgo White Sox, Chicago Cubs, and Baltimore Orioles
Kevin Garnett when he played for the Minnesota Timberwolves
Nick Markakius- Outfielder Baltimore Orioles
He chose the number 21 because it is the number of letters in his full name. (Roberto Clemente Walker)
Because Washington Redskins Safety Sean Taylor was shot and killed and his number was 21. So, every team in the NFL wears that on the back of their helmets.