The phrase "from ancient grudge break to new mutiny" comes from the prologue of William Shakespeare's play Romeo and Juliet. In this context, it refers to the longstanding conflict between the Montague and Capulet families (the "ancient grudge") that erupts into new violence and conflict (the "new mutiny").
The phrase suggests that the deep-seated hatred and animosity between these two families, which has persisted over time, is igniting fresh battles and chaos. The use of "mutiny" implies rebellion and upheaval, indicating that the conflict is not just a continuation of old grievances but is also becoming a more active and destructive struggle in the lives of the characters involved. Overall, the line encapsulates the theme of how inherited conflict can lead to new problems and tragedies.