LaMelo Ball Trashes Vegas House During Crazy Indoor Water Balloon Fight

Lonzo Ball's 15-year-old brother, LaMelo, unleashed a sneak water balloon attack on two girls in bikinis -- INSIDE the Vegas home where he's staying -- while wearing a shirt with his own face on it.

Yep.

It all went down Sunday night -- and yeah, Lonzo was inside the home as the water fight broke out. It was a mess. Water everywhere. Ketchup. Craziness.

Unclear if Lonzo is footing the bill for the pad (probably, since he's the only one getting a paycheck) -- but he didn't seem to care as his 15-year-old lil bro destroyed the house.

There was one moment where LaMelo grabbed a loaded pillowcase and swung it at one of the women -- but smartly put it down and splashed her with water instead. Careful, dude.