There is much more to this story, no telling what was said by the deceased to the officers, no telling what he was attempting to do with his hands either which started the struggle.
Maybe the officers had reason to believe he was armed, maybe an officer felt what he thought was a gun and the deceased began reaching for it, thats when the struggle started and then an officer fearing for their safety fired.
Remember the courts have said that officers do not have to await the glint of steel to be in fear of life or limb.
If he was unarmed, they didn't have to fear his limb.
The only glint of steel they would have seen in this case would have been from the handcuffs that the shootee had attached to his wrists behind his back.