زَيْدٌ فِي الدَّارِ قَائِمًا
Translation: Zayd is in the house, standing.
زَيْدٌ: nominative topic.
فِي: preposition.
الدَّارِ: genitive after fī.
فِي الدَّارِ: prepositional phrase attached to an understood predicate (e.g., mustaqirr).
قَائِمًا: accusative ḥāl describing Zayd, governed by the understood sense of being situated.
Qāʾiman is not the predicate accidentally made accusative: the location supplies the predicate, while qāʾiman adds a circumstance.