Question

Throw the Book at Someone to punish severely for breaking rules or the law; to give the maximum penalty

Accepted Answer

Dan was expelled for writing on the walls. They really threw the book at him. In this idiom the "book" is the law book, filled with all the penalties that a judge can impose on the wrongdoer. Imagine a judge figuratively throwing that whole, heavy law book at an offender of the law, hitting him or her with the worst possible punishments. That image was in the mind of the writer who coined this expression many years ago.

Idiom	Throw the Book at Someone
Example	Dan was expelled for writing on the walls. They really threw the book at him.
Meaning	to punish severely for breaking rules or the law; to give the maximum penalty
Origin	In this idiom the "book" is the law book, filled with all the penalties that a judge can impose on the wrongdoer. Imagine a judge figuratively throwing that whole, heavy law book at an offender of the law, hitting him or her with the worst possible punishments. That image was in the mind of the writer who coined this expression many years ago.

Book Law Judge Throw Dan Expelled Writing Walls