Dak Prescott is lucky his dogs are still alive ... TMZ Sports has obtained video of the day the QB's pets allegedly attacked his neighbor -- and it shows a cop had an assault rifle trained on the animals with a finger on the trigger.
It all went down on Feb. 25, when two of Dak's pit bulls managed to escape his Frisco, Texas home ... and made their way down the street to a neighbor's yard.
Officials say the dogs chewed through the neighbor's fence ... attacked her dogs -- and when she tried to intervene, one of the pit bulls chewed off the top of her finger.