'Big Bro' Star Busted Again - Witness Intimidation

The "Big Brother" star who allegedly beat his pregnant girlfriend was arrested again last week -- after his GF told cops he was trying to scare her into dropping the charges.

According to the Winthrop Police Department's incident report, Matt McDonald and his family members allegedly waged a relentless 2-day campaign of intimidation against the accuser and her family ... after Matt's initial arrest on April 18.

In the report, Matt's GF claims she began to feel frightened when Matt began calling her from jail -- 4 times in 48 hours.

The GF also claims that Matt's family began to harass her -- first on the phone ... and then they started showing up at her work ... demanding that she drop the charges.

Matt was eventually arrested for witness intimidation on April 23 -- after cops determined he may pose a serious threat.

Attempts to reach Matt for comment were unsuccessful.