Fall from the highest pile but no head injuries! (6)
I believe the answer is:
topple
'fall' is the definition.
(I know that topple is a more specific form of the action fall)
'highest pile but no head injuries' is the wordplay.
I cannot really understand how this works, but
'highest' could be 'top' (at the top) and 'top' is located in the answer.
This explanation may well be incorrect...
'from the' acts as a link.
Can you help me to learn more?
(Other definitions for topple that I've seen before include "Overthrow, cause to fall" , "Overthrow or fall headlong" , "Knock off perch" , "(Cause to) tip over" , "Knock (from power?)" .)