Restriction can fall on the agent, object, or another verbal complement, not only on a subject and predicate in a nominal sentence. In a pattern with mā and illā or with innamā, one must determine which constituent is selected and which competing constituent is excluded.
«مَا ضَرَبَ إِلَّا عَمْرًا زَيْدٌ»
Zayd struck only ʿAmr, and no other object.
In this arrangement the selected element functions as the object. A differently arranged construction such as “mā ḍaraba ʿAmran illā Zayd” can focus the agent instead: it was Zayd who struck ʿAmr. Parsing the clause prevents the direction of restriction from being reversed.