جَاءَنِي الضَّارِبُ زَيْدًا.
Translation: The person who strikes Zayd came to me.
جَاءَ is the main past verb; «نِي» includes a first-person object pronoun.
الضَّارِبُ is nominative as the subject of «جَاءَ»; in the classical analysis, al- is relative and «ضَارِب» is its active-participle ṣilah with an implicit returning subject.
زَيْدًا is the object governed by the active participle «ضَارِب», not an object of «جَاءَ».