Where troops have only a single wound, casualties are removed as follows. If a unit of troops is hit and suffers wounds which it does not save then for each wound, one model is removed as a 'kill'. Although it is convenient to think of casualties as slain, individual warriors are not necessarily dead, they may be temporarily knocked out, incapacitated, or simply too badly wounded to carry on fighting. For our purposes, the result is the same so we treat all casualties as if they were killed and remove them.
Although casualties would really fall amongst the front rank, for the purposes of gameplay remove models from the rear rank of the unit. This keeps the formation neat and represents rear rankers stepping forward to cover gaps in the line. If the unit is deployed in a single rank then casualties are removed roughly equally from either end, representing the troops gathering about their leader and standard.