Exegesis:

The force of the three imperfects etupton, eneptuon, prosekunoun, ‘they were beating,’ ‘they were spitting,’ ‘they were doing homage,’ is that of actions repeated by several soldiers.

tuptō (only here in Mark) ‘strike,’ ‘beat.’

emptuō (cf. 10.34) ‘to spit on.’

proskuneō (cf. 5.6) ‘to worship,’ ‘to reverence,’ ‘to do homage’: here in mockery, as to a king (cf. Gould, Rawlinson).

kalamō (15.36) ‘with a stalk,’ ‘with a reed,’ ‘with a staff.’

tithentes ta gonata (only here in Mark; cf. gonupeteō 1.40; 10.17) ‘bend the knees,’ ‘kneel down’: perhaps the Greek equivalent of the Latin genua ponere.

Translation:

The reed was evidently used as a flail with which to beat Jesus over the head, thus pounding the crown of thorns deeper into his flesh. One may have to translate ‘beat him on the head with a reed’ (or ‘stick’ or ‘staff’) or ‘flailed him on the head….’

The imperfect form of the Greek verbs translated struck, spat, and knelt justify the translation of ‘repeatedly struck … spat … and knelt’ or ‘one after another struck … spat … and knelt.’

Knelt down in homage may require the addition of a qualifier so as not to lead to misinterpretation, e.g. ‘knelt down as though honoring’ or ‘got down on their knees, pretending to show respect.’

Quoted with permission from Bratcher, Robert G. and Nida, Eugene A. A Handbook on the Gospel of Mark. (UBS Handbook Series). New York: UBS, 1961. For this and other handbooks for translators see here .