Exegesis:

ti gar epoiēsen kakon; ‘why, what evil (thing) has he done?’: in such a question gar means ‘why!’ ‘how so!’

kakos (cf. 7.21) ‘evil deed,’ ‘bad thing.’

perissōs (cf. 10.26) ‘exceedingly,’ ‘all the more.’

Translation:

Said to them may require modification to ‘asked them.’

Why may be expanded slightly in order to be an equivalent expression of concern, e.g. ‘why so’ or ‘why say that.’

What evil has he done may be paralleled by ‘what sin has he committed’ or ‘what bad deed has he done.’

All the more is a kind of comparative, indicating at the same time a high degree of activity, e.g. ‘yelled more, more’ or ‘shouted so much greater.’

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 .