The Wicket-keeper reference article from the English Wikipedia on 24-Apr-2004
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Wicket-keeper

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The wicketkeeper in cricket is the fielding player who stands behind the batsman on strike at the wicket

His major function is to stop balls that pass the batsman (to prevent a run or runs} but also to attempt to dismiss the batsman in various ways. Most common dismissal is for the keeper to catch a ball that has nicked the batsman's bat, called an edge, before it bounces. The keeper can also "stump" the batsman by using the ball to remove the bails from the stumps if the batsman is out of his crease after a delivery.

When the ball is hit into the outfield, the keeper moves close to the stumps to catch the return throw from a fielder and, if possible, to run-out a batsman.

The wicketkeeper is the only fielder allowed to touch the ball with protective equipment, typically large webbed and padded gloves and leg pads. but these are not always adequate. Famous England wicketkeeper Allan Knott sometimes placed steaks inside his gloves for added cushioning.