TMZ Sports has obtained police video from Errol Spence Jr.'s horrifying Ferrari crash which shows a cop scrambling to get a blood sample from the boxer while he was being treated at the hospital.
... plus, the footage also shows officers found a loaded, expensive handgun at the crash scene.
As we previously reported, Spence -- one of the best boxers in the world -- wrecked his Ferrari during an Oct. 10 crash that was captured on video.
It's a miracle the 29-year-old survived ... 'cause the car was ripped to shreds -- and the dude was EJECTED from the vehicle after impact.