Key somebody turned a lot, oddly (7)
I believe the answer is:
pivotal
'key' is the definition.
(I've seen this in another clue)
'somebody turned a lot oddly' is the wordplay.
'somebody' becomes 'vip' (I've seen this in another clue).
'turned' says the letters should be written in reverse.
'oddly' indicates an anagram (letters in an odd order).
'vip' written backwards gives 'piv'.
'a'+'lot'='alot'
'alot' is an anagram of 'otal'.
'piv'+'otal'='PIVOTAL'
(Other definitions for pivotal that I've seen before include "Key" , "Crucially important" , "Central - decisive" , "Of central importance" , "Crucial, critical" .)