Chainsaw

"DIE, DIE, MY DARLINGS!!!! DIE, DIE, DIE!!!"

- Ellis

The Chainsaw is a special close combat weapon, introduced in Left 4 Dead 2.

Official Description
Realize every zombie killer’s dream with the ultimate in gore-splattering destruction. But the fun won’t last forever—once the gas gauge hits E, it’s useless.

Melee Mechanics
Just like other melee weapons, the Chainsaw replace your pistols in the side-arm slot. They have to be used in conjunction with the primary weapon to form a fitting group. Unlike pistols, the close combat weapons never need to be reloaded. Despite this, the Chainsaw can run out of fuel and cannot be refilled by any means. The drawback to melee weapons is that they do not reach very far, and cannot be relied on entirely. The Chainsaw is the only close combat weapon that can cause massive friendly fire damage to the Survivors and caution should be exercised, particularly on Advanced and Expert levels, where there is no clemency.

Damage wise, the Chainsaw is the weapon with the highest damage per second. The Chainsaw has the unique ability to slay a Tank in the fastest time of eight seconds (in Expert). The Chainsaw can kill the Witch in Easy before she is startled, and a Common Infected in just one hit (regardless of whether it damages the head, similar to normal melee weapons). The Special Infected generally need less than half a second against the Chainsaw, aside from the Charger which takes just over half a second. However, it is still suggested that you do not melee the Boomer or Spitter, as their deaths affect the radius of their corpse and the melee weapon positions you close enough to be hit.

The Chainsaw is classified as a Shredding weapon, and will spew blood on your screen as it mutilates Infected.

Tactics

 * Against Boomers and Spitters, it's best to use your primary weapon.
 * The Chainsaw's long deploying time, in which it must be revved up, means that switching to it in the middle of a horde is a bad idea. Instead, find some cover before pulling it out, or just momentarily back to a wall and shove the horde back when revving up.
 * Be careful against Tanks and other Special Infected that pin you, as if you are knocked down, you have to rev up your Chainsaw again after getting up, leaving you vulnerable for a longer period of time.
 * Tap primary fire when using the Chainsaw against small groups of Common Infected to save fuel.
 * When covered in Boomer bile, the Chainsaw is a good option to rip through the incoming horde. Communicate with your team-mates, so that you don't accidentally cut them.
 * Keep your distance from other Survivors when using the Chainsaw so to avoid hurting them and make it easier for them to shoot Common Infected attracted to you.
 * When using the Chainsaw, it's usually best to pick up a primary weapon with good range, such as an Assault Rifle or Sniper Rifle, for taking out Special Infected and pulling off distance shots.
 * The Grenade Launcher and Chainsaw don't work too well together, because the Chainsaw has a long rev-up time, while the Grenade Launcher has a long reload time. They're also both difficult to find, cannot refill ammunition, do heavy friendly fire damage, and leave you without a viable long range weapon.
 * A Bile bomb works well with the Chainsaw, making it easy to line up Infected for kills. Be prepared to kill the extra Common Infected summoned by the bile, however.
 * When fighting a Tank, using the Chainsaw usually results in being punched away. Wait for the Tank to be stumbled, climbing, picking up concrete, or punching another Survivor before rushing in to slice him.
 * The Chainsaw is the only melee weapon that will allow you to free yourself from a Smoker's tongue while being initially grabbed, as well as before being grabbed, as a preventative measure. Other melee weapons can prevent the tongue from attaching to you just before it hits, but it requires very precise timing along with knowing which direction the tongue came from. The Chainsaw does not require any particular aiming or such precise timing; simply use the Chainsaw either before being attacked by the Smoker's tongue (to cut it as it wraps around you) or as you are caught (to free yourself).
 * When trying to kill a Witch with a Chainsaw, be sure to attack her from behind so that she must turn before being able to retaliate. This will buy you enough time to kill her even on Expert.
 * The Chainsaw does not consume fuel while idling.
 * Try to conserve Chainsaw fuel for special needs. Examples are Crescendo Events (especially Gauntlet Crescendos), Witch, Tanks or random hordes.
 * The Chainsaw's size and the smoke generated when attacking can heavily impede your vision. This, coupled with the disorienting blood that covers the screen when ripping through a horde, can cause you to take damage more often than when using a different melee weapon. Stay calm and steady your aim.
 * Due to the noise, using the Chainsaw will attract nearby Common Infected toward you.

Pros

 * Fastest attacking melee weapon
 * Heavy damage at high rate of speed
 * Perfect against Hordes, the Witch (if done behind) and many other Special Infected, like the Smoker
 * Probably the best melee weapon against a Tank, if two Survivors carries Chainsaws
 * If empty, switches to a single P220 Pistol
 * No consumption of fuel when not attacking

Cons

 * Limited fuel and usage; gets discarded when empty
 * Long deploying time, leaving you vulnerable
 * Not useful to have if carrying a Special Tier weapon like the Grenade Launcher
 * Creates a lot of smoke, impedes your vision
 * Rare; difficult to find
 * Not so useful against lone Common Infected
 * Heavy damage means the same in friendly fire, use with caution