This option is not available to ordinary prisoners, but to lords and nobles without exception. To do this, go to the party menu, select the prisoner and click on "Execute Prisoner" . The decision to execute should be carefully considered. Before you do that, however, you should be aware...
Sergeant System –Commanders now designate units to other lords in battle, including the player! Execute the orders issued by your commander throughout the fight, and use your own instincts to do your part and help secure victory on the field of battle. Lead the horse archers as they skirmish...