It is hard to beat the IRS in court.
Hammer tried and failed. He filed for bankruptcy way back in the day and believe that took care of all of his tax debt.
In fact, it did wipe away $1.5 million of it, but the IRS claimed that he owed another $800k for 1996 and 1997 that were not included in his bankruptcy (Hammer should sue his lawyers for forgetting that).
The judge ruled in favor of IRS and Hammer has to pay up.