9 Grk “in/by which,” referring to the change of behavior described in v. 3. The unbelievers are astonished by the readers’ moral transformation. Because of the length and complexity of the Greek sentence, a new sentence was started here in the translation.
10 Or “are surprised, are taken aback.” The same verb occurs in 4:12.
11 Grk “blaspheming,” giving the result of their astonishment. Here the target of their “blasphemy/vilification” is not God but the Christian.

In other versions

With respect to this they are surprised when you do not join them in the same flood of debauchery, and they malign you;

They are surprised that you do not join them in their reckless, wild living, and they heap abuse on you.

They are surprised that you don’t join them in the same flood of wild living—and they slander you.

Of course, your former friends are surprised when you no longer plunge into the flood of wild and destructive things they do. So they slander you.

with respect to which they are surprised when you do not run with them into the same flood of dissipation, and so they revile you.

Wherein they think it strange that ye run not with them to the same excess of riot, speaking evil of you:

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