ضُرِبَ زَيْدٌ — Zayd was struck.
ضُرِبَ: past passive verb, built on fatḥa, from active «ضَرَبَ».
زَيْدٌ: nāʾib al-fāʿil, nominative with visible ḍamma.
The doer of the striking is not named. Although Zayd is grammatically nominative, he is the receiver of the action, not its semantic agent.