Build battlements when Norman's head is found in basket, dead (10)
I believe the answer is:
crenellate
'build battlements when' is the definition.
I can't judge whether this defines the answer.
'norman's head is found in basket dead' is the wordplay.
'head' suggests taking the first letters.
'is found in' is an insertion indicator.
'basket' becomes 'creel' (basket for holding fish).
'dead' becomes 'late' (similar in meaning).
The initial letter of 'normans' is 'n'.
'n' going inside 'creel' is 'crenel'.
'crenel'+'late'='CRENELLATE'
Can you help me to learn more?
(Another definition for crenellate that I've seen is " Provide with battlements".)