Miami Marlins Ball Boy Commits Epic Blunder, Hurls Fair Baseball Into Stands

A ball boy broke the first rule of being a ball boy at the Marlins game Thursday ... grabbing a live baseball in fair play and chucking it into the stands -- costing his team a run.

The epic blunder went down in the sixth inning of Miami's tilt with the Los Angeles Dodgers in Florida ... after Freddie Freeman roped a liner down the right-field line.

The ball flew over first base and skidded into the outfield ... but for some reason, the ball boy in the area thought it had landed in foul territory.

The guy nonchalantly jogged over to the ball, scooped it up, and then hurled it to some fans in the crowd.

Of course, there were big ramifications for the act ... umps allowed Mookie Betts to score -- not knowing if the play would have been made by Miami's right fielder had the ball boy not interrupted.

It ultimately didn't matter too much in the end ... the Marlins got rocked, 10-0 -- and even Miami outfielder Jesús Sánchez came over to let him know it was OK.