SWAT 4 features a single-player campaign where the player has to take his SWAT team through a number of missions. The missions are not related and there is no overarching storyline. The game aims to have gameplay similar to the real SWAT team experience, for example, it encourages the use of non-lethal weapons to subdue and arrest the suspects rather than shooting them dead. On the higher difficulty levels, it is impossible to progress to the next mission if the current one is not done well, such as suspects getting killed instead of arrested or other team members getting shot.

The player is the leader in a five-man SWAT team, which consists of him and four other men that can be split into two teams of two (called red and blue). The player does not assume direct control over the other officers, however, he can issue them orders such as guard an opening, entering and clearing a room (while at the same time using assorted grenades), handcuff suspects, and so on.

All missions start with a pre-mission briefing which describes the situation and gives whatever details are available on the subjects and/or hostage(s) or other civilians. The briefing also identifies mission goals, which typically are to secure (arrest or kill) all suspects and rescue the hostages or other civilians. Mission objectives are not limited to these, however. After the briefing, the player can choose equipment for himself and the other four officers, for some missions choose an entry point, and then the mission starts.

Usually the player then tries to resolve the situation in such a way as to arrest all the suspects, rescue all the civilians, and secure all the weapons - if that is done and no one is injured in the process, the mission is completed with a perfect score. The missions have very different suspects. Some are poorly armed and unarmored, and these are easy to arrest with the use of no or only non-lethal weaponry. Suspects in the later missions, however, include ones with fully automatic weapons such as AK-47s. Suspects may also be better protected by things such as gasmasks and full body armor. If it is not possible to arrest a suspect, then the team is forced to kill or "neutralize" the suspect.

SWAT 4 also has the concept of authorized and unauthorized use of weapons. Most situations require the officers to give the suspect a warning and ask him to surrender. Shooting without warning is considered unauthorized use of force or deadly force (depending on whether you injure the suspect or kill him) and has a significant point penalty for the mission. Shooting without warning is allowed if the suspect is pointing his weapon at a hostage or a SWAT team member or if he opens fire first. Suspect reactions to warnings differ - some may attempt to hide and set up and ambush, some immediately surrender, others will flee and some will open fire. If a hostage is killed, it results in immediate mission failure.

Source: Wikipedia Article