Mattingly joined the Marlins after parting ways with the Los Angeles Dodgers last year after five seasons.
Mattingly didn't ban facial hair when he was manager of the Dodgers -- but grooming policies aren't completely unheard of for MLB clubs.
Red Sox outfielder and part-time caveman Johnny Damon went from sporting hefty facial hair to getting rid of it completely in 2005 after signing with the historically strict New York Yankees in the offseason.
Mattingly played his entire 14-year major league career with the Yankees, often sporting a mustache that'd make even Tom Selleck jealous.
"Remember back in 1991 (the old folks do) when Don Mattingly refused to cut his hair? He was benched for that. Good thing he never played for anyone who banned facial hair," an ESPN anchor jokes.
Oh, how the tables have turned.
RELATED: 25 best baseball players of last 25 years
25 best baseball players of last 25 years
Miami Marlins' new manager outlaws facial hair on players
Craig Biggio, Roy Halladay, Trevor Hoffman, Mike Mussina, Joe Mauer, Clayton Kershaw, Felix Hernandez, Jeff Bagwell, Eric Gagne, CC Sabathia, Tim Hudson, Chase Utley, Nomar Garciaparra, Miguel Tejada, Juan Gonzalez, Mark Buehrle, Roy Oswalt, Andy Pettitle, Curt Schilling, Bobby Abreu, Andrew McCutchen, Carlos Beltran, Edgar Martinez, Johan Santana, Jason Giambi, Raphael Palmiero, Barry Larkin, Fred McGriff.
(The Sporting News via Getty Images)
25. Mike Trout
Rookie of the Year, MVP, 4-time All-Star
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24. Jim Thome
600+ home runs, 5-time All-Star, 72.9 bWAR
(BRIAN BAHR via Getty Images)
23. John Smoltz
200+ wins, 150+ saves, 8-time All-Star
(Doug Pensinger via Getty Images)
22. Frank Thomas
2-time MVP, 4-time All-Star, 500+ home runs
(TIM ROBERTS via Getty Images)
20. David Ortiz
9-time All-Star, 3-time World Series champion, 400+ home runs