A.T. Robertson Commentary John 18:22

"And when he had said this, one of the officers standing by struck Jesus with his hand, saying, Answerest thou the high priest so?" — John 18:22 (ASV)

When he had said this (ταυτα αυτου ειποντος). Genitive absolute of second aorist active participle of ειπον, to say.

Standing by (παρεστηκως). Perfect active (intransitive) participle of παριστημ (transitive), to place beside. One of the temple police who felt his importance as protector of Annas.

Struck Jesus with his hand (εδωκεν ραπισμα τω Ιησου). Late word ραπισμα is from ραπιζω, to smite with a rod or with the palm of the hand (Matthew 26:67). It occurs only three times in the N.T. (John 18:22; John 19:3), in each of which it is uncertain whether the blow is with a rod or with the palm of the hand (probably this, a most insulting act). The papyri throw no real light on it. "He gave Jesus a slap in the face." Cf. 2 Corinthians 11:20.

So (ουτως). As Jesus had done in verse 21, a dignified protest in fact by Jesus.