A more thorough explanation:

Antithetarius (an-tith-uh-tair-ee-uhs) is a term from Law Latin that refers to an accused person who claims that their accuser is actually guilty of the crime they are being accused of. This is different from an approver, who is a person who confesses to a crime and implicates others in order to receive a lighter sentence.

For example, imagine that John is accused of stealing money from his employer. John claims that his accuser, Sarah, is actually the one who stole the money and is trying to frame him. In this case, John would be considered an antithetarius.

Another example could be a situation where a person is accused of assault, but claims that the alleged victim actually attacked them first and they were acting in self-defense.

The examples illustrate the definition of antithetarius by showing how an accused person can use this defense strategy to shift the blame onto their accuser. By claiming that the accuser is actually guilty of the crime, the accused is attempting to create doubt in the minds of the judge and jury and avoid being convicted. However, this defense can be difficult to prove and may require strong evidence to support the claim.