Overthrows look simple until the ball reaches the boundary or the batters cross more than once. Then the exact moment of the throw matters, because that decides which runs are added.
Start with the boundary allowance, normally four. Next add every run the batters completed before the instant of the throw or other act that sent the ball to the boundary. Finally add the run they were attempting at that instant only if they had already crossed. For example, suppose one run was complete and the pair had crossed on their second when a throw was released and then reached the rope. The boundary overthrow produces six in total: four for the boundary, one completed run, and the crossed run in progress. Runs completed after the release do not replace that snapshot; the law fixes the calculation at the act that caused the boundary.
A genuine overthrow follows a deliberate throw at a wicket or toward another fielder. A ball that merely deflects or is accidentally kicked to the rope can be treated differently because the special completed-runs calculation is tied to a throw or wilful act. MCC has clarified this distinction in the Laws edition scheduled for 1 October 2026. Until that edition applies, use the current Law and the competition's playing conditions, especially where a deflection sits close to the line between a misfield and a deliberate act.
After awarding the runs, the umpires must place the batters at the correct ends. Their positions when the ball becomes dead, the number of runs allowed, and whether they had crossed at the relevant instant can all matter. That is why two plays adding the same number to the score may leave different batters on strike. Work through the crossing and the boundary award in order rather than using the simple shortcut that an even total always preserves the striker.
If the pair had not crossed when the fielder released the boundary-bound throw, the run then in progress is excluded from the special boundary calculation. The batters might visibly complete it before the ball reaches the rope, but the earlier snapshot still governs. Conversely, crossing before the throw can add that run even though neither batter reached the opposite crease before the boundary. This is why the replay must find both the release frame and the moment the batters passed one another.
That can still become more than one if the overthrow goes for four. The law does not ignore the running that was already earned before the ball reached the boundary.