To step backwards in part of shoe (6)
I believe the answer is:
toecap
'part of shoe' is the definition.
('toecap' is part of 'shoe')
'to step backwards' is the wordplay.
'step' becomes 'pace' ('pace' can be a synonym of 'step').
'backwards' shows that the letters should be reversed in order.
'pace' written backwards gives 'ecap'.
'to'+'ecap'='TOECAP'
'in' acts as a link.
(Other definitions for toecap that I've seen before include "Boot's metal end" , "Protective front of boot" , "Boot or shoe item" , "Reinforced covering at top of shoe" , "piece of footwear" .)