It's the quick timing that you need to be able to hand off at the exact time the runner is ready to receive it. The runner has already started toward the line and expects the ball to be in his gut. Any hesitation by either will result in a mishandle and likely a fumble. I'm not saying he's too slow, he could also be too fast and it would result the same. Usually requires a first step and some guys just pull the ball out from center and turn without the step. Probably just hasn't had enough snaps to get comfortable.