fail to deliver the best defense ในทางกฎหมาย หมายความว่าอะไรคะ

จากประโยคนี้ค่ะ

They knew that he was innocent, but they could not reveal that information without violating the principle of attorney-client privilege. Had they done so, they would have failed to deliver the best defense they could muster for their client.

ขอบคุณค่ะ