Many nicked, almost all turning up (4)
I believe the answer is:
lots
'many' is the definition.
(lots of something)
'nicked almost all turning up' is the wordplay.
'nicked' becomes 'stole' (nick can mean to steal).
'almost all' means to remove the last letter (most but not all of the word).
'turning up' says the letters should be written backwards.
'stole' with its last letter removed is 'stol'.
'stol' written backwards gives 'LOTS'.
(Other definitions for lots that I've seen before include "Units sold at auctions - plenty of them" , "Oodles" , "Loads" , "may be drawn" , "Large numbers at auction" .)