We turned against wickedness, showing physical strength (5)
I believe the answer is:
sinew
'physical strength' is the definition.
(I've seen this before)
'we turned against wickedness' is the wordplay.
'turned' says the letters should be written backwards.
'against' is a charade indicator (letters next to each other).
'wickedness' becomes 'sin' (synonyms).
'we' in reverse letter order is 'ew'.
'ew' after 'sin' is 'SINEW'.
'showing' is the link.
(Other definitions for sinew that I've seen before include "Cord of tissue connecting muscle to bone" , "Strength; tendon" , "It indicates strength" , "Inelastic tissue" , "Tough connective tissue" .)