This can be stated in active form. Alternate translation: "when his soldiers kill some of your men" (See: [[rc://en/ta/man/translate/figs-activepassive]])
The noun "slaughter" means an event where many people are brutally killed. This can be expressed as a verb. Alternate translation: "Many of the soldiers who follow Absalom have been slaughtered" or "The enemy soldiers have killed many of the soldiers who follow Absalom" (See: [[rc://en/ta/man/translate/figs-abstractnouns]])