<P> In his autobiography Bill Haywood described Idaho miners held for, </P> <P>... months of imprisonment in the bull - pen, a structure unfit to house cattle, enclosed in a high barbed - wire fence . </P> <P> Penned up in bullpens as a response to violence, many hundreds of union men had been imprisoned without trial . Peter Carlson wrote in his book Roughneck, </P> <P> Haywood traveled to the town of Mullan, where he met a man who had escaped from the bullpen . The makeshift prison was an old grain warehouse that reeked of excrement and crawled with vermin . Overcrowding was so severe that some two hundred prisoners had been removed from the warehouse and quartered in railroad boxcars . </P>

Where did the name bullpen come from in baseball