Scott couldn't have tased the officer. The taser had already been fired, and the model he had isn't a multi-shot unit. One and done. And the taser prongs were in Scott.
so just to recap what you can read in the trial blog - slager tazed scott by firing the tazer, he then tried multiple more times to taze him while they struggled by using the "unloaded" tazer as a direct contact stun gun, and then he lost control of the taser and the defense claims scott tazed slager using the direct contact method, and that even when scott fled again and was at a distance slager still feared the tazer could be used against him and he could have his gun taken.
(the tazer can be reloaded but i dont see any evidence that it was)