Albert Barnes Commentary Deuteronomy 19:16

"If an unrighteous witness rise up against any man to testify against him of wrong-doing," — Deuteronomy 19:16 (ASV)

Testify against him that which is wrong - The margin note, more literally, states “a falling away.” The word is used (Deuteronomy 13:5) to signify apostasy or revolt; here it is no doubt to be understood in the wider sense of any departure from the Law.