The under-fire News International boss had the bizarre office accessory when she was editor of Rupert Murdoch's Sun newspaper.
Staff say she would paste the faces of people who had annoyed her to it and punch them – and invite others to do so.
The unfortunate targets of her wrath could be anyone from the prime minister to a junior reporter who had failed to meet her expectations.
An ex-senior reporter at the Sun said: “It was bizarre, bordering on the unhinged.
“Whatever the outcome of the hacking scandal the punch-ball gives you an idea of the ultra-aggressive culture she presided over as editor of The Sun.”
The bizarre revelation came on the day Brooks faced the Commons Culture, Media and Sport Committee's investigation into phone hacking.
During questioning about her tenure as editor of the News of the World she said she had repeatedly been assured that allegations the newspaper hacked into phones were untrue.
And she appeared to backtrack on her 2003 comments that payments had been made to the police saying: “I can say that I have never paid a policeman myself. I have never sanctioned, knowingly sanctioned, a payment to a police officer.”