仗义 is a separable verb (离合词) meaning to act out of a sense of loyalty or justice, especially toward friends. It carries a strong cultural association with 义气 (brotherhood loyalty) in Chinese interpersonal ethics. As a v.o. structure, you can insert elements like 了, 过, or measure words between the characters: 仗了义, 仗过一次义. The object (e.g., 朋友) is typically introduced by 对 or 为 before the verb, not after it.