en_tn/2sa/18/07.md

The army of Israel was defeated there before the soldiers of David

This can be stated in active form. Alternate translation: "There the soldiers of David defeated the army of Israel" (See: rc://en/ta/man/jit/figs-activepassive)

a great slaughter

an event where many people are brutally killed

twenty thousand men

"20,000 men" (See: rc://en/ta/man/jit/translate-numbers)