Give up protecting virtuous head? How could you? (3,8,4)
I believe the answer is:
for goodness sake
'how could you?' is the definition.
'give up protecting virtuous head?' is the wordplay.
'give up' becomes 'forsake' (I've seen this before).
'protecting' indicates putting letters inside.
'virtuous head?' becomes 'goodness' (I can't justify this - if you can you should give a lot more credence to this answer).
'forsake' placed around 'goodness' is 'FOR GOODNESS SAKE'.
(Other definitions for for goodness sake that I've seen before include "Words of exasperation" , "Really!" , "please!" .)