LeBron James -- Royal Penis Exposed ... During NBA Finals

LeBron James didn't go balls out in Game 4 of the NBA Finals ... he went dong out instead.

Moments before tip off Thursday night, LeBron went to adjust himself below the waist ... and it just so happened to be at the same time an ABC camera moved in for a close-up.

James opened his shorts a little too much ... and boom -- LeBron's penis was introduced to roughly 18.5 MILLION viewers.

If you really wanna see it ... click here -- but WARNING, it's a penis.