The law is unfortunately ambiguous. I can see an interpretation where it's five, but can also see one where it's six. 19.8 Overthrow or wilful act of fielder If the boundary results from an overthrow or from the wilful act of a fielder, the runs scored shall be any runs for penalties awarded to either side and the allowance for the boundary and the runs completed by the batsmen, together with the run in progress if they had already crossed at the instant of the throw or act. So we have a boundary that has happened as a result of Guptil's overthrow/act. Under the law, it would clearly be 4 runs allowance for the boundary. There would also clearly be the first run that was completed before Guptill's throw. So that is five. The ambiguous part is the second run attempted by the batsmen. The preamble of the law above says "if the boundary results," so a lot of lawyers (including me) would assume that the law is drafted for application at the time the ball went over the rope. Under that logic, the second run attempted by the batsmen is a completed run, not an in-progress run. This is because at the time the ball crossed the boundary, Stokes was safely in his crease and the batsmen stopped running). There's no in-progress run in this interpretation. However, if the second run attempted by the batsmen should be interpreted as an in-progress run, then then the batsmen clearly had not crossed at the time of the throw. In this scenario NZ got hosed.