Legendary NBA player Bill Russell was arrested for taking a loaded gun through airport security.
The 11-time NBA champ was breezing through security at Sea-Tac International Airport in Seattle Wednesday ... when a screener noticed something funny in his carry-on. Turns out ... Bill was packin' a fully loaded, .38 caliber Smith & Wesson handgun.
He could be fined up to $7,500.
Russell -- who became the first Black coach in the NBA -- got the Presidential Medal of Freedom in 2011, courtesy of Barack Obama.
We reached out to Russell for comment ... so far, no word back.