Run (one's) mouth phrase
If you "run your mouth", you talk non-stop and nonsense, especially in an annoying way.
He kept running his mouth until his mom got really angry.
Katherine admitted that her tendency to run her mouth could get her into trouble
The young lady has run her mouth since the early morning.
The verb "run" should be conjugated according to its tense.
To decide to believe someone‘s saying although they may not tell the truth
He said that he was late because he had an accident and I gave him the benefit of the doubt.