LiAngelo Ball wondered if his stealing incident in China was the reason he didn't get selected in the NBA draft ... saying, "the sh*t I did off the court" might have cost him.

It all went down in the latest episode of the family's Facebook docuseries, "Ball In The Family" ... where cameras caught the middle Ball bro's reaction to not being picked to join Lonzo in the Association.

"I don't know, I guess it's the way I play, I guess," Gelo says of why he thinks he didn't get drafted.

"Or the sh*t I did off the court."

Of course ... Gelo -- along with 2 teammates from UCLA -- were detained in China after stealing several pairs of designer sunglasses and other accessories from multiple stores in Hangzhou.

LiAngelo was suspended from the Bruins indefinitely ... and LaVar eventually pulled him from school to play ball in Lithuania.