Cut up joint that's not top grade (5)
I believe the answer is:
shred
'cut up' is the definition.
(I've seen this in another clue)
'joint that's not top grade' is the wordplay.
'joint' becomes 'shared' (eg in joint ownership).
'that's not' is a deletion indicator (that has not).
'top grade' becomes 'A' (top academic grade).
'shared' with 'a' removed is 'SHRED'.
(Other definitions for shred that I've seen before include "Bit; cut or tear into tiny strips" , "Rip up" , "Torn piece of material" , "Small part" , "just a touch" .)