Pinned into wrong desk? Used to be (8)
I believe the answer is:
skewered
'pinned' is the definition.
(skewering is a kind of pinning)
'into wrong desk? used to be' is the wordplay.
'into' means one lot of letters goes inside another.
'wrong' indicates anagramming the letters.
'used to be' becomes 'were' (I've seen this before).
'desk' anagrammed gives 'sked'.
'sked' placed around 'were' is 'SKEWERED'.
(Other definitions for skewered that I've seen before include "Transfixed" , "Spiked" , "Pierced through with meat pin" , "Run through" , "Red's week (anag)" .)