en_tn/jdg/20/36.md

The men of Israel had given ground to Benjamin, because they were trusting in the men ... outside Gibeah

From this sentence until the end of verse 41 is background information that the writer inserted to explain to the readers how the ambush defeated the Benjamites. (See: rc://en/ta/man/jit/writing-background)

had given ground to Benjamin

This is an idiom that means they intentionally retreated. Alternate translation: "had allowed Benjamin to move forward" (See: rc://en/ta/man/jit/figs-idiom)