وَهِيَ أَيْ «هَلْ» تُخَصِّصُ الْمُضَارِعَ بِالِاسْتِقْبَالِ
Hal directs the imperfect verb toward future time.
The Arabic imperfect may in itself refer to the present or future. One recognized property of hal is to orient an imperfect toward future time. Thus “Hal taḍribu Zaydan?” ordinarily asks whether the addressee will strike Zayd.
Hamza is not restricted in exactly this way: “A-taḍribu Zaydan?” can, with a suitable context, question an action occurring now. As always, the actual context determines how an example is understood.