When the players’ “clocks” are synced, if there is e.g. a 4 frame packet round trip time between them, each player should be 2 frames ahead of the time of the last received input from their opponent. Players should normally experience 2 frame rollbacks.

If one player lags behind, the other player will receive inputs from farther “in the past” than they should. This can be up to 15 frames. This can cause unnecessarily big rollbacks and artificial lag. The player that’s behind may even be receiving inputs that appear to be “in the future” to their game and never experience rollbacks at all.