What violent conflict occurs when Hindley returns home in Chapter 9?

Hindley enters drunk and stumbling, and Hareton hides from his father, who is either savagely affectionate or violently angry. Heathcliff, who has been waiting for an opportunity to exact revenge on Hindley, loses his chance when his reflexes and sudden impulse make him grab the boy. Heathcliff is angry and Hindley is angry, but Hareton seems unhurt.