Can peek excitedly, seeing a bit of leg (7)
I believe the answer is:
kneecap
'a bit of leg' is the definition.
('kneecap' is part of 'leg')
'can peek excitedly' is the wordplay.
'excitedly' is an anagram indicator (letters excited or stimulated into a new form).
'can'+'peek'='canpeek'
'canpeek' with letters rearranged gives 'KNEECAP'.
'seeing' acts as a link.
(Other definitions for kneecap that I've seen before include "Bone" , "The informal patella (7)" , "Horribly punish" , "one going on bender?" , "part of joint" .)