Johnny Manziel's mom refused to take a Breathalyzer and failed a field sobriety test just before she was thrown behind bars last week for DWI ... law enforcement sources tell TMZ Sports.
Michelle Manziel's run-in with cops took place in Kerrville, Texas at around 10 PM on March 1 ... after we're told Kerrville Police Department officers noticed she was driving with a busted tail light.
During an ensuing traffic stop, our sources say Michelle showed signs of intoxication .