In جَاءَ زَيْدٌ مُسْرِعًا, Zayd is the subject and bearer of the circumstance. In رَأَيْتُ زَيْدًا مُبْتَسِمًا, Zayd is the object, yet it is his state that the accusative ḥāl describes. A bearer of ḥāl is therefore not restricted to grammatical subjects.
When a following circumstantial clause contains a pronoun, its referent must be a syntactically and semantically suitable participant. Mistaking that referent leads to the wrong decision about whether a linking wāw is needed.
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Appendix to Faṣl and Waṣl: Circumstantial Clauses, Wāw and Pronominal Linkage
In جَاءَ زَيْدٌ مُسْرِعًا, Zayd is the subject and bearer of the circumstance. In رَأَيْتُ زَيْدًا مُبْتَسِمًا, Zayd is the object, yet it is his state that the accusative ḥāl describes. A bearer of ḥāl is therefore not restricted to grammatical subjects.
When a following circumstantial clause contains a pronoun, its referent must be a syntactically and semantically suitable participant. Mistaking that referent leads to the wrong decision about whether a linking wāw is needed.