Kingpin begins with Woody Harrelson as Roy Munson, a child bowling prodigy who won the 1979 Iowa state amateur championship. Young Roy is all set to leave his tiny hometown of Ocelot, Iowa to go on the professional bowling tour. He wins his first tournament, defeating a none-too-pleased established pro named Ernie McCracken (Bill Murray) in the finals. Roy receives an oversized check and the enmity of McCracken.
The unhappy McCracken decides to get back at the young bowler, first by putting sugar in his gas tank, then convincing him to join him in a bowling-alley hustle while sitting at the diner where he heckles the waitress (Linda Carola). Munson needs money to repair his car engine, so he agrees. The scheme goes horribly awry when their "marks" realize they've been hustled. Roy is abandoned by the opportunistic McCracken and the angered marks shove Roy's right hand into a ball-return, amputating it.
In the present, a down-and-out Munson, sporting a prosthetic hook which he covers with a fake rubber hand, sells bowling alley supplies with little success. He lives in a seedy apartment building in Scranton, Pennsylvania along with a wino who wants to die, a man who drinks his own urine, and a landlady who is constantly after Roy because he never pays his rent on time.
On a sales call, Munson catches sight of Ishmael Boorg (Randy Quaid) rolling a respectable game. Munson tries to get him to turn pro, since he claims to have a "265 or 270" average. The Amish man has little interest in worldly affairs, though. He isn't even supposed to be bowling, as it is against Amish tradition, and he reluctantly admits it is the only "vice" he and his grandfather enjoy.