From coinsite.com:
[Querying person writes]: I have a 1951 Lincoln head cent. The only error I can find wrong with it is that the 1 in the date is severely slanted. I do not know what caused the error, and I was wondering if there was a price for such an error.
[Site responds]: This is a common effect of damage from the device that pulls coins through a counting machine. The metal is actually bent at the surface by the tongue that moves the coin. This damage does not constitute an “error” nor does it increase the value of the damaged coin.