Seedy guy regularly getting nervous (4)
I believe the answer is:
edgy
'nervous' is the definition.
('edgy' can be a synonym of 'nervous')
'seedy guy regularly' is the wordplay.
'regularly' means one should take alternating letters (regularly take one letter, leave next etc.).
'seedy'+'guy'='seedyguy'
The alternating letters of 'seedyguy' are 'EDGY'.
'getting' is the link.
(Other definitions for edgy that I've seen before include "Challengingly experimental" , "Visibly nervous" , "Nervous and tense, irritable" , "Anxious" , "Nervous; jumpy" .)