IMHO, from the video, bad shoot.
The security guard escalated the situation and, by what was seen, initiated physical conflict. When his level of force, likely not necessary, was insufficient, and the target thereof tried to defend himself, he shot the man.
Arguably, the deceased man's actions were defensive, not offensive, until after the man had been hit with a two-handed baton blow.
Use of force was initiated by the shooter, who was visibly (well, audibly) angry, and who continued to escalate force until the death ensued.