Second line in Pinter's sharp piece (8)
I believe the answer is:
splinter
'sharp piece' is the definition.
'splinter' can be an answer for 'piece' (thesaurus). I also know that 'sharp' relates to this answer.
'second line in pinter's' is the wordplay.
'second' becomes 's' (common abbreviation).
'line' becomes 'l' (used when specifying particular lines from a poem).
'in' means one lot of letters goes inside another.
'l' going into 'pinter' is 'plinter'.
's'+'plinter'='SPLINTER'
(Other definitions for splinter that I've seen before include "Shard" , "Sharp wood fragment, painful in flesh" , "Needle-like piece of wood" , "Sliver of wood, sore in the flesh" , "Small, sharp sliver" .)