Prosecutors ain't going down in their case against Robert Kraft without a fight ... they just filed docs saying a judge was wrong to bar them from using the graphic sex spa video in court.
78-year-old Kraft scored a huge victory in the case last May, when a judge ruled police surveillance video of him allegedly receiving sex acts inside the Orchids of Asia spa in Florida could NOT be used in the case.
The judge claimed when cops executed their search warrant and planted cameras inside the spa ... they didn't do enough to protect people who were inside the spa getting perfectly legal massages.