Someone has to be injured. It just picks one whoever replaces the DC. The game result is fixed, nothing will change it. The goals are fixed, the injuries, assists...all pre-determined before the commentary. Make whatever changes you want...you had a DMR on and change your formation so that you dont need a DMR, but the DMR was supposed to be injured in the pre-game, so whoever you replace the DMR with will be the one that is injured, whether it is a ST or MC. The once the commentary is over, it makes the necessary changes to the personnel based on the managers changes during the commentary and the result is set in stone.