Rollback netcode is a networking technique where the game predicts the opponent's inputs, simulates the game forward immediately, and then rewinds and replays if the prediction was wrong. On each frame, the game saves a snapshot of the state, applies predicted inputs, and renders. When the real inputs arrive and differ from the prediction, the game rolls back to the saved state, applies the correct inputs, and fast-forwards through all the frames to catch up to the present. The result feels dramatically more responsive than delay-based netcode, which simply freezes the game for a few frames while waiting for remote inputs. The technique became famous in the fighting game community through GGPO middleware, and the push for rollback in every fighting game has become one of gaming's most successful community advocacy campaigns.