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Knocking-in is a process done to new cricket bats to compress the wood and allow them to be ready for use, as most brand-new cricket bats will crack or badly dent if used in competition without being knocked-in.
The Knocking-In Process
After the application of a thin layer of linseed oil the person knocking in the bat must use either a worn-down 'soft' leather cricket ball or a specialised mallet and hit the face of the blade of the bat repeatedly for several hours. After three to four hours of knocking in, another layer of linseed oil may be applied. At this stage the bat may be used in light practice but should not be used in competition without another few hours of knocking-in. The spring of the bat should not be knocked as this will cause the bat to jar.
After being properly knocked in, the wood will make a slightly higher-pitched sound when hitting the ball and will feel softer to use.
Testing the willow
During the knocking-in process, a fingernail is pressed into the front face of the bat to check if the bat is properly knocked in. If an indentation is left on the bat during this process, it shows that the wood is still not fully compressed, and should be knocked in for longer.
Many large sports stores and specialised cricket stores use special machines to knock in the bats for customers. Some manufacturers will roll the bats through a special press to compress the wood, however many bat manufacturers choose not to do this as the spring may be rolled as well, causing jarring.
Many bats that claim to be pre-knocked-in by the manufacturer should be manually knocked in anyway as this claim is not a guarantee that the bat is ready to be used in competition.