Parsing of قَامَ زَيْدٌ:
1. قَامَ: perfect verb, built on fatḥ. Meaning: “stood.”
2. زَيْدٌ: fāʿil, nominative; its visible nominative sign is the ḍamma at the end.
3. The verb and its fāʿil together form a verbal sentence.
Why this case? The action of standing proceeds from Zayd, so he is the fāʿil. The tanwīn with ḍamma also reflects that زَيْدٌ is a fully declinable noun.