Tear to bits
I believe the answer is:
'tear to bits' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for shred that I've seen before include "Torn-off fragment" , "Strip of material; a very small amount" , "Cut into bits" , "Bit; cut or tear into tiny strips" , "Tatter; small amount" .)