There are reports of this trophy being glitchy, it also requires a significant amount of luck.
I got this in a TDM match in the map "Hell's Kitchen", there are poles placed throughout the level and I killed two people in one life by throwing the pole at them, the trophy popped for me after I was eventually killed.
You don't need to do this in one life, just in the one match. What's important is that the object you killed the first person with has to be the same object you kill the second person with.