Black Friday's ending - grabbing special treat will cause bodily harm (7)
I believe the answer is:
battery
'bodily harm' is the definition.
'black friday's ending grabbing special treat' is the wordplay.
'black' becomes 'b' (as in pencil classifications).
'ending' says to take the final letters.
'grabbing' is an insertion indicator.
'special' indicates an anagram.
The last letter of 'friday' is 'y'.
'b'+'y'='by'
'treat' with letters rearranged gives 'atter'.
'by' enclosing 'atter' is 'BATTERY'.
'will cause' is the link.
(Other definitions for battery that I've seen before include "Accumulator" , "Power cell" , "Storage cell" , "Equipment for war" , "Power source; artillery unit" .)