كَمْ رَجُلٍ ضَرَبْتَهُ!
كَمْ: declarative, in the nominative topic position.
رَجُلٍ: genitive tamyīz.
ضَرَبْتَ: past verb with subject tāʾ; هُ is the object pronoun referring back to the man.
ضَرَبْتَهُ: verbal clause functioning as the predicate of kam.
This matters because the verb is already occupied by its resumptive object pronoun, so kam is not its direct object.