Combat is very similar to that of the later Grand Theft Auto series. You aim, fire and hopefully kill your enemy. The game isn't based on stats or dice rolls, it's based on player skill.
Much to the delight of my inner villain, you can run people over with your vehicle. You can also crash your vehicle into shops to bust out the front window and loot the contents for a quick sale at a local pawn shop. As an Enforcer, you will be alerted (via an APB that flashes on your screen) about a crime in progress. It's your job to hunt down the criminal and either arrest or kill them, according to the quest objectives.
This is how missions work in APB, introducing a mechanic that plunges you into the action head-first. Once the objectives of the mission are met, you will receive special rewards, based on several factors, such as number of objectives completed and notoriety level of the enemies. Notoriety and threat are used in APB to measure how good you are at your job. As an Enforcer, you want to be the best at nabbing crooks and as a Criminal, you want people to know they can't mess around with Jim. There's also a witness mechanic in place to increase threat when one of more NPC citizens see you committing a crime. As a criminal, you can commit so many crimes that your threat stars are at five, causing a bounty to be placed on your head and your location to be visible to all Enforcer players. Once that bounty is collected, your threat will go back down to three stars. This threat level rises and falls throughout the game based on your actions and cooldown time.Rewards unlock new customization options, but since the game has no classes or levels, you won't find any type of level grind necessary. These rewards aren't based on time invested, either. You only win rewards when you win the objective and losing gets you nothing. That way, everyone has a fair chance in the game.
Ammunition is something that you'll need to keep a close eye on throughout battles. You can purchase boxes of ammo, grenades and other weapons even during a mission. Not all weapons are lethal, though. Enforcers have access to stun weapons to be used for arresting and subduing Criminals.
Arresting is an interesting mechanic that's only available to Enforcers. It's a way to use non-lethal force to immobilize players for 30 seconds. When you kill someone, they respawn 200 meters away in 6 seconds, so you can see how arrests would be a bit more frustrating for the arrested.