Focus involved taking Navy line - derisive (8)
I believe the answer is:
scornful
'derisive' is the definition.
(I've seen this before)
'focus involved taking navy line' is the wordplay.
'involved' indicates an anagram (involved can mean confusing or complex).
'taking' indicates putting letters inside.
'navy' becomes 'RN' (abbreviation for Royal Navy).
'line' becomes 'l' (used when specifying particular lines from a poem).
'focus' is an anagram of 'scofu'.
'scofu' going around 'rn' is 'scornfu'.
'scornfu'+'l'='SCORNFUL'
(Other definitions for scornful that I've seen before include "Contemptuous or derisive" , "Disdainful, contemptuous" , "Dismissive, contemptuous" , "sneering?" , "Mocking" .)