Star sign giving protection to a shrewish woman (6)
I believe the answer is:
virago
'shrewish woman' is the definition.
(a virago is a shrewish or domineering woman)
'star sign giving protection to a' is the wordplay.
'star sign' becomes 'virgo' (I've seen this before).
'giving protection to' indicates putting letters inside (inserted letters are given protection).
'virgo' placed around 'a' is 'VIRAGO'.
(Other definitions for virago that I've seen before include "Termagant" , "Harridan" , "noisy woman" , "Scolding or domineering woman" , "Strong and aggressive woman" .)