on someone's back

on (one's) back

Constantly nagging one about something. Ugh, my mom is on my back all the time about my grades, but I just have no interest in the classes I'm taking this semester.
See also: back, on
Farlex Dictionary of Idioms.

on someone's back

Also, on someone's case. See under off someone's back.
See also: back, on
The American Heritage® Dictionary of Idioms by Christine Ammer.

on someone's back

If someone is on your back, they are criticizing you a lot or trying to persuade you to do something. The crowd aren't forgiving — as soon as you make a mistake they're on your back. If they find out you're weak, they're on your back straight away. Compare with get off someone's back.
See also: back, on
Collins COBUILD Idioms Dictionary, 3rd ed.
See also:
  • be on (one's) back
  • be on somebody's back
  • be on someone's back
  • back at it
  • back at it (again)
  • back onto
  • back onto (something)
  • a fire extinguisher
  • (a body part) is killing (one)
  • a whole thing