Toss head showing lack of confidence (7)
I believe the answer is:
shyness
'lack of confidence' is the definition.
(I've seen this before)
'toss head' is the wordplay.
'toss' becomes 'shy' (both can mean to throw).
'head' becomes 'ness' (ness is a headland).
'shy'+'ness'='SHYNESS'
'showing' is the link.
(Other definitions for shyness that I've seen before include "lack of confidence" , "Nervousness, timidity" , "Timid behaviour" , "Reserve" , "Diffidence" .)