Bad temper shown by fisherman dropping line (5)
I believe the answer is:
anger
'bad temper' is the definition.
(thesaurus)
'fisherman dropping line' is the wordplay.
'fisherman' becomes 'angler' (angler is a kind of fisherman).
'dropping' indicates named letters should be taken away.
'line' becomes 'l' (used when specifying particular lines from a poem).
'angler' with 'l' taken out is 'ANGER'.
'shown by' is the link.
(Other definitions for anger that I've seen before include "Rage" , "Irk" , "Emotion" , "Spleen" , "wind up?" .)