Beckett DeJean Blew .142 On Breath Test During OWI Arrest, Cops Say

Cooper DeJean's brother, Beckett, allegedly had a BAC well above the legal limit when he was arrested for operating while intoxicated over the weekend -- cops say he blew a .142 on a breath test.

TMZ Sports has obtained 20-year-old DeJean's arrest affidavit ... with cops stating the former South Dakota defensive back was "unable to maintain lane" as he was driving his Chevy Malibu around 11:55 PM on Saturday. Once he was pulled over, the officer claimed "a strong odor of alcohol." was evident.

The cop said as they searched his vehicle for a source of the odor, a case of beer was present in the backseat ... and once questioned, DeJean admitted to drinking.

DeJean was taken to the Ida County Sheriff's Office for field sobriety tests, which cops say he failed, and he was placed under arrest.

He blew into a DataMaster device to measure his BAC ... and the results, according to cops, were .142, which is over the .08 legal limit.

In the docs, officials also say DeJean had bloodshot/watery eyes, smelled like alcohol and struggled with his balance during the arrest.