The changing of a present tense in direct speech to a past tense in reported speech
The changing of a present tense in direct speech to a past tense in reported speech (or a past tense to pluperfect).
Example: 'If the sentence starts in the past, there is often backshift of tenses in Reported speech.'
Links:
https://www.oxforddictionaries.com/definition/english/backshift
Also see:
What is "backshifting", as applied to English grammar?