Jermall Charlo has been arrested ... after cops say the boxing superstar melted down at a bar and stole money from a waitress, TMZ Sports has learned.
The alleged incident all went down in San Antonio on July 16 -- the day before Charlo's brother, Jermell Charlo, fought Brian Castaño to a draw at AT&T Center.
According to police documents, Jermall was with a large party at the Texas bar when the waitress presented the group with the bill.