TMZ Sports has obtained the 911 call made by Joseph Randle's ex -- in which she claims the Dallas Cowboys running back pointed a gun at her and her son ... and threatened to kill them.

The call was made on February 4th ... during an incident at a hotel in Wichita, Kansas.

The woman on the phone, who has a child with Joseph, told the operator Randle had gone ballistic.

"He put his hands on a female ... he pointed a gun in front of the mother of his child," she said.

"He was threatening me to take our lives ... we have our child with us."

The woman says Joseph was also in possession of a bunch of weed -- which he was trying to ditch when he learned cops were on the way.

The woman also claims Randle put the gun in a car, which left the scene before officials arrived.

A short time later, the woman called 911 again and changed her story -- telling cops she and Randle had "talked it out" and that everything was fine.

During the 911 call, which was released by authorities, the operator explained that he couldn't call off the cops because she mentioned a gun.

Randle was eventually arrested for marijuana possession -- a charge that was later dropped.