Very important charge raised over a pile up (9)
I believe the answer is:
paramount
'very important' is the definition.
I can't judge whether this definition defines the answer.
'charge raised over a pile up' is the wordplay.
'charge' becomes 'rap' (both can mean blame or responsibility).
'raised' is a reversal indicator (going up in a down clue).
'over' means one lot of letters go next to another (in a down clue, some letters go over others).
'a pile up' becomes 'amount' (I can't explain this - if you can you should believe this answer much more).
'rap' back-to-front is 'par'.
'par'+'amount'='PARAMOUNT'
Can you help me to learn more?
(Other definitions for paramount that I've seen before include "outstanding" , "First" , "Predominant" , "Highest" , "More important than anything else" .)