1Ch 13:9-10 And when they came unto the threshingfloor of Chidon, Uzza put forth his hand to hold the ark; for the oxen stumbled. And the anger of the LORD was kindled against Uzza, and he smote him, because he put his hand to the ark: and there he died before God.

That's a bit harsh when he was just trying to save the ark falling off. For that matter couldn't God have stopped it falling? maybe he wasn't paying attention