Dozens of cops flooded a Bronx courtroom Tuesday as an NYPD sergeant went on trial for shooting dead a mentally ill, bat-wielding Bronx woman.

Some of the officers held a large blue banner outside the courtroom that read “#weareforbarry’’ — while others wore blue caps with gold lettering with the same words — to show their support for Sgt. Hugh Barry, who is charged with murdering Deborah Danner, 66.

Barry had been responding to a radio call for an “emotionally disturbed person — violent’’ when he and other officers arrived at Danner’s Castle Hill home the night of Oct. 16, 2016.

He spotted Danner, a schizophrenic, wielding scissors in her bedroom, court papers have said. The sergeant said Danner then grabbed a bat and lunged at his head and that he shot her in self-defense.

Prosecutors have said in court documents that Barry “disregarded his training from the New York City Police Department in dealing with emotionally disturbed persons . . . by rushing into Ms. Danner’s apartment without getting critical information.’’

Critics say he should have at least tried to taser Danner first.