In the sport of cricket, a bouncer is a type of delivery, usually bowled by a fast bowler. It is pitched short so that it bounces on the pitch well short of the batsman and rears up to chest or head height (or even higher) as it reaches the batsman.
Bouncers are used tactically to drive the batsman back on to his back foot if he has been freely playing front foot scoring shots such as drives. To this end, bouncers are usually directed more or less at the line of the batsman's body. Note that, in contrast to baseball, aiming at the batsman is not illegal, and is a tactically useful part of the game.
To effectively deal with a bouncer, the batsman must primarily avoid being out, and secondarily avoid being hit by the ball. For a head-high bouncer, these goals are achieved most easily by ducking under the ball. If the ball is at chest height, the batsman's best defence is to move on to his back foot, raise his bat vertically to chest height, and attempt to block the ball and direct it downwards to the pitch so as to avoid presenting a catch to a fielder. Sometimes the batsman will need to jump into the air to gain the necessary height to defend with the bat, this is true in many shorter batsmen like Sachin Tendulkar
Given these approaches, the bowler can hope to both intimidate the batsman somewhat and possibly have the ball deflect off the bat at an awkward angle and produce a catch for a nearby fielder.
Because of the potential danger to batsmen of being hit and to stop bowlers bowling bouncers all the time, there are laws in the Laws of Cricket governing how frequently a bowler may bowl bouncers. These laws take into account the relative skill of the batsmen.
The deliberate and sustained bowling of bouncers aimed at the body was a tactic used by Australia in 1932/33, dubbed the Bodyline series by the Australians. This dangerous tactic caused the Laws of Cricket to be reformed to prevent any recurrence.