On New Year’s Eve 1984, Allen lost control of his Corvette and crashed into a stone wall on the side of the road in the English countryside after flying into a fit of road rage. His left arm was severed during the horrific wreck. Doctors initially reattached Allen's arm, but because of infection, it was removed again permanently. Allen eventually adapted a new method of playing the drums and helped design an electronic kit he could play using only one arm. He made his post-accident debut in 1986 when Def Leppard headlined the Monsters of Rock festival in England. The next year, the band released Hysteria, the biggest album of their career so far, selling over 20 million copies worldwide.