This isn’t just for Police Officers. We hear the reason to be verbal is to get the attention of potential helpers, witnesses, protect ourselves from the media, etc.
However, the reason for verbalizing is far more important than this: it keeps us BREATHING. The number one issue we have with people learning to defend themselves is that they hold their breath while fighting. This is normal under stress as we get so focused on the mission we forget to breath. By giving verbal commands to the attacker we keep ourselves breathing. To do this correctly, use short, one word commands; STOP (strike), GET (strike), BACK (strike), etc. If the commands are too long, you will run out of breath. We will give another important reason for verbal commands next time. Until then, Be safe, Be A.W.A.R.E. (TM)