Daft onlooker after leaving name has now left (7)
I believe the answer is:
witless
'daft' is the definition.
(I've seen this before)
'onlooker after leaving name has now left' is the wordplay.
'onlooker' becomes 'witness' (I've seen this before).
'after leaving' suggests deleting specific letters.
'name' becomes 'n' (common abbreviation e.g. on forms).
'has' is an insertion indicator.
'now left' becomes 'l' (common abbreviation. I am not sure about the 'now' bit.).
'witness' with 'n' taken out is 'witess'.
'witess' enclosing 'l' is 'WITLESS'.
Can you help me to learn more?
(Other definitions for witless that I've seen before include "Daft" , "Foolish, stupid" , "Out of one's mind (maybe scared)" , "Lacking sense, understanding or judgment" .)