"Throw the book at" is an idiomatic expression that means to impose the maximum penalty or punishment for an offense committed by someone. This phrase can be replaced by its antonyms, which are "be lenient," "be merciful," or "go easy on." These terms refer to a compassionate or forgiving approach towards the offender. For instance, instead of throwing the book at a first-time offender, a judge might decide to be lenient and give probation or community service instead of prison time. In conclusion, using the opposite of "throw the book at" can help convey a more positive and humane attitude towards those who have made mistakes.