punch ‧ bag /ˈpʌntʃbæɡ/ BrE AmE British English , ˈpunching bag American English noun [countable]
1 . a heavy leather bag hung from a rope, that is punched for exercise or training
2 . a person who is hit, criticized strongly, or blamed, even though they have done nothing wrong:
a young wife whose husband used her as a punching bag