Blac Youngsta Says Lil Pump's Gun Arrest is BS

Lil Pump and his mother are getting a raw deal from law enforcement ... according to his homie, Blac Youngsta, who has some choice words for cops. Three to be exact.

We got Youngsta outside Ciroc Studios in Hollywood, and he took a break from plugging his new record to support Pump. TMZ broke the story ... Pump was arrested for firing a handgun while in his L.A. apartment. The 17-year-old rapper's mom could also be in trouble for leaving a minor home alone with a gun and weed.

Youngsta thinks law enforcement's version of the story is total BS, and didn't pull punches when we asked for his opinion.

We'd say BY is starting the "Free Lil Pump" campaign, but Pump got out of jail yesterday -- with a GPS ankle monitor -- and bragged about his "rich lawyer."