off one's rocker

村上春樹の短編 'Honey Pie' を読んでいます。
Over the next five years, he was nominated four times for the Akutagawa Prize, but he never won it. He remained the eternally promising candidate. A typical opinion from a judge on the prize committee would say: "For such a young author, this is writing of very high quality, with remarkable examples of both the creation of scene and psychological analysis. But the author has a tendency to let sentiment take over from time to time, and the work lacks both freshness and novelistic sweep." Takatsuki would laugh when he read such things. "These guys are off their rocker. What the hell is 'novelistic sweep'?..."
芥川賞の候補に挙げられたが、結局受賞していない村上春樹自身の話の様に思われます。
上の引用文に出てきた慣用句らしい "off their rocker" の意味を辞書で調べます。
・Oxford English Dictionary: Insane: When his attempts to do so fail miserably, Phillip starts to go off his rocker.
・Collins Dictionary: Crazy; insane.: He's off his rocker if he thinks he can tackle the whole thing alone.
・Merriam-Webster's Online Dictionary: in a state marked by extreme confusion or mental unsoundness: he felt dizzy, slightly off his rocker at this extraordinary assailment of his senses
語源も気になるのでOnline Etymology Dictionaryを見ると次の説明がありました。
Slang off (one's) rocker "crazy" first recorded 1897. Meaning "one who enjoys rock music"