In Gridlocked, David Hendrix is a former leader of a special forces police force. He has had to leave special forces because of medical problems, so he is now a regular cop.
In the movie we see him patrol with a fashion actor, who has been “awarded” his superiors. Possibly the actor has some role in what he has to do as a police officer and wants to see how they work, or he gets bored and wants to get tough for a day.
When they are patrolling they receive a call. A police training center is being attacked by terrorists. It is a very serious thing, so David goes there to take the actor with him.
Taking advantage of his experience in combat, David will be in charge of organizing the resistance, in order to endure until more reinforcements arrive, while eliminating all the terrorists they can to be able to release the training center.