וַיָּבֹ֖אוּ עַד־גֹּ֣רֶן נָכ֑וֹן וַיִּשְׁלַ֨ח עֻזָּ֜א אֶל־אֲר֤וֹן הָֽאֱלֹהִים֙ וַיֹּ֣אחֶז בּ֔וֹ כִּ֥י שָׁמְט֖וּ הַבָּקָֽר׃
Giunsero fino all'aia di Nacon; e Uzzà stese la mano verso l'Arca di Dio e la afferrò, perché i buoi l'avevano fatta scivolare.
Rashi
ונדחה ידו AND HIS HAND MOVED (SLIPPED) when he was about to let the axe fall upon the tree. The Targum rendering is ותתמריג ידה, the meaning being, “his hand moved itself to let the stroke of the axe fall upon the tree”. The words (II Samuel 6:6) כי שמטו הבקר are rendered in Targum Jonathan on by: ארי מרגוהי תוריא “for the oxen moved it (the Ark)”
Rashi
drove the cart as is the custom of cart drivers, one walks in front of the cart and directs it in a straight way, and one is alongside the cart, so that it does not turn over and fall. And so it is written (II Sam. 6: 4): “... and Ahio went before the Ark,” and Uzza was alongside the cart; therefore, Uzza stretched forth his hand to take hold of the Ark when the oxen swayed it, and therefore, he was punished.