LaVar Ball's mouth might've finally written a check his ass can't cash, because Shaq has accepted the Big Ballers' challenge, and he's putting his dome on the line for victory.

This all got started when we got Shareef O'Neal out at LAX and asked him if he thought he could beat LaMelo Ball in a 1-on-1 battle. He said "Yes," and his father, the Big Diesel, agreed.

The news made it back to LaVar ... and of course he didn't back down, offering to end the speculation with a 2-on-2 game, Shaq and Shareef, vs. LaVar and LaMelo.

Well, Shaq  -- wearing a hilarious white wig -- made a video message to respond to LaVar, and he's in ... saying if his fam loses, he'll glue the white wig to his head for good.

Challenge accepted. Is the T-Mobile Arena available?!