Spikes crack large and small walls (5)
I believe the answer is:
laces
'spikes' is the definition.
('lace' can be a synonym of 'spike')
'crack large and small walls' is the wordplay.
'crack' becomes 'ace' (I've seen this before).
'large' becomes 'l'.
'and' is a charade indicator (letters next to each other).
'small' becomes 's' (abbreviation - e.g. clothes size).
'walls' means one lot of letters goes inside another (to 'wall' can mean to contain).
'l'+'s'='ls'
'ace' going within 'ls' is 'LACES'.
(Other definitions for laces that I've seen before include "Cords for fastening shoes" , "Shoe ties" , "Scale for boot fasteners" , "Scale for shoe securers" , "Cords for tying shoes" .)