زَيْدًا ضَرَبْتُ
It was Zayd whom I struck.
If the listener believes ʿAmr, not Zayd, was struck, fronting Zayd can reverse that erroneous judgment. This is qasr al-qalb: the wrongly assigned participant is replaced by the correct one.
The point is not simply to assert that striking occurred. The communicative dispute concerns which person was struck. A rhetorical classification must track that dispute.