Due to many negative factors, for example, blood clotting, stunning
without any reason is Makrooh (reprehensible). (Shaami vol.6 pg.296; HM
If the animal is wild and uncontrollable, then only will one be excused for
stunning the animal. The sacrifice will be valid only if the animal was
alive at the time of slaughtering after the stunning.
From: Al Mahmood 13 Q & A from the Darul Ifta
Mufti Ebrahim Desai