Boss tells a whopper about son’s latest pieces of news (9)
I believe the answer is:
'pieces of news' is the definition.
'boss tells a whopper about son's latest' is the wordplay.
'boss' becomes 'head' ('head' can be a synonym of 'boss').
'tells a whopper' becomes 'lies'.
'about' is an insertion indicator.
'latest' indicates one should take the final letters.
The final letter of 'son' is 'n'.
'lies' enclosing 'n' is 'lines'.
(Other definitions for headlines that I've seen before include "Captions of newspaper articles" , "linked with furrowed brows?" , "News stories" , "is star performer" , "Starts of newspaper articles" .)