Ex-'DWTS' Contestant Was Busted for DUI

More legal trouble for ex-boxing champ Victor Ortiz -- who was arrested for DUI in California over the weekend ... TMZ Sports has learned.

We've confirmed ... the 29-year-old movie star and former "Dancing With the Stars" contestant was arrested on Saturday evening.

Law enforcement sources say Ortiz was pulled over in a BMW around 7 PM for expired registration tags -- and when the officer approached the car, they suspected Ortiz was hammered.

He then bombed field sobriety tests and was arrested for misdemeanor DUI.

He was booked and has since been released. We reached out to Ortiz, but so far no official comment.

Here's the real problem for Ortiz -- he's already on probation stemming from a 2015 battery at a Kenny Chesney concert at the Rose Bowl.