Did you read what happened? The DEA was about to move to make an arrest when a vehicle in front of the residence pulls away with it's lights off. The obvious interpretation of those events is the target of the raid is trying to flee. When you then intercept the car, the car rams 2 of your vehicles and then drives at an agent.
This wasn't a Bonny and Clyde ambush where the cops just started shooting. If the car had come to a stop, even after ramming the first car, there wouldn't have been a shooting.