This can be translated in active form. Alternate translation: "the Philistines defeated the Israelites and killed" (See: [[rc://en/ta/man/translate/figs-activepassive]])
Here the number four thousand is a round number. There may have been a few more than that or a few less than that. The word "about" shows that it is not an exact number. Alternate translation: "about 4,000 men" (See: [[rc://en/ta/man/translate/translate-numbers]])