مَا ضَرَبْتُ زَيْدًا — I did not hit Zayd.
● مَا gives negation.
● ضَرَبْتُ is the past verb; its ending also identifies the speaker as the subject.
● زَيْدًا remains the object.
Negation changes the truth of the action, not the grammatical roles already present in the sentence.