12:21 PM PT -- Mantei appeared in front of a judge (over a livestream) in Berrien County, Michigan ... and plead not guilty to misdemeanor domestic violence.
MM was given a personal recognizance bond ... meaning he will be discharged from county jail without paying any money.
He is due back in court May 2.
Flame-throwing ex-MLB pitcher Matt Mantei was arrested and thrown in jail for assault and battery Tuesday night in Michigan ... TMZ Sports has learned.
Mantei -- a closer with a 100 MPH heater -- played 10 seasons in the big leagues for the Marlins, Diamondbacks and Red Sox.