Convict to fall behind (3)
I believe the answer is:
lag
This clue is a double definition.
'convict' is the first definition.
(thesaurus)
'fall behind' is the second definition.
('lag' can be a synonym of 'fall behind')
'to' is the link.
(Other definitions for lag that I've seen before include "Fall behind with a convict" , "Old convict - dally - insulate" , "Wrap to protect from frost" , "person inside" , "Ex-convict" .)