And on that day represents the longer Hebrew expression, which indicates the beginning of a new paragraph, as in verse 6 and verse 8. It should be translated in the same way as in those verses.

A great panic from the LORD shall fall on them: Panic is an emotional reaction that causes great fear and confusion (compare 12.4 and 1 Sam 14.20). In some languages it may be more natural to restructure this clause to say “the LORD will send a great panic on them,” “the LORD will throw them into a great panic” (Bible en français courant, Parola Del Signore: La Bibbia in Lingua Corrente), or “the LORD will make them so confused and afraid” (Good News Translation). Them refers to the enemies attacking Jerusalem, as in verse 12.

So that each will lay hold on the hand of his fellow: The rest of the verse describes the result of the panic. The expression lay hold on the hand of is in itself neutral, and does not indicate whether the action is friendly (compare 8.23) or hostile. However, in the present context, and especially in the light of the next clause, most translators have understood that the action is hostile, and have translated it so. In English the appropriate hostile sense is supplied by using verbs like “seize” (Moffatt, New American Bible, Good News Translation, New International Version, New Revised Standard Version), “snatch” (New Jewish Publication Society’s Tanakh), and “grab” (Jerusalem Bible/New Jerusalem Bible, Beck). The only exception is New English Bible, which has “At the very moment when a man would encourage his comrade.” This interpretation is unconvincing, however, and Revised English Bible has replaced it by rendering the last half of the verse as “everyone laying hands on his neighbour and attacking him.” Translators are advised to interpret the action of laying hold of the other person as hostile, and to translate it accordingly.

And the hand of the one will be raised against the hand of the other: This rendering is unnaturally literal. The meaning is expressed simply and clearly as “they will attack each other” (New International Version). Other effective renderings are “they will hit out at each other” (Jerusalem Bible), “they will fall to fighting among themselves” (New Jerusalem Bible), and “They will fight against each other in hand-to-hand combat” (New Living Translation for the last two clauses).

Quoted with permission from Clark, David J. & Hatton, Howard A. A Handbook on Zechariah. (UBS Helps for Translators). New York: UBS, 2002. For this and other handbooks for translators see here .