مَا ضَرَبَ عَمْرًا إِلَّا زَيْدٌ
No one struck ʿAmr except Zayd.
Although the object ʿAmr is overtly mentioned, nominative Zayd is the agent after illā. The exclusivity therefore concerns who performed the action, not the identity of the person struck.
Comparative review
DeviceRhetorical contribution
لاAffirms then denies a rival
بلTurns toward a replacement assertion
لكنCorrects a preceding expectation
ما…إلاExplicit negation followed by exception
إنماCompact restrictive particle