Nightstick

 "♪ Gonna beat me a zombie to death with a nightstick~ ♪" -Ellis

The Nightstick (or Tonfa) is a new close-combat weapon introduced in Left 4 Dead 2.

The Nightstick takes the slot of the Pistols, and kills Common Infected in one hit. Compared to most other melee weapons, it seems to have a faster attack rate, and like every other melee weapon it has a cleaving effect that can hit multiple close-range targets with one swing. It's usually found in certain safe rooms or randomly throughout levels, but the Nightstick can also be dropped by a Riot Infected when killed, if there's one around his waist.

The Nightstick isn't really supposed to be used against Special Infected, however. Against Boomers, Spitters, and Witches, it isn't very effective, while against Hunters, Smokers, and Jockeys it's better to shoot them, and it takes two hits to kill a Charger while putting you at high risk of taking high damage from the Charger's melee attack. It can, however, be marginally effective against a Tank who is pounding another player.

Trivia

 * Although the Survivors call it a nightstick, the proper name for this weapon is a Tonfa.
 * In the original Left 4 Dead, many Infected police officers have nightsticks hanging from their belts, though they can not be picked up upon their death.
 * The weapon is or strongly resembles a Monadnock PR-24 police baton, commonly associated with law enforcement officers. It can be distinguished from a true Tonfa in that it is not made of wood and is used alone rather than in a pair.