Arms smuggler is a jolly good sprinter (9)
I believe the answer is:
gunrunner
'arms smuggler' is the definition.
(I've seen this before)
'jolly good sprinter' is the wordplay.
'jolly good' becomes 'gun' (I can't explain this - if you can you should believe this answer much more).
'sprinter' becomes 'runner' (to sprint is to run fast).
'gun'+'runner'='GUNRUNNER'
'is a' is the link.
Can you help me to learn more?
(Other definitions for gunrunner that I've seen before include "one secretly moves pieces?" , "Arms smuggler" , "one who moves arms impermissibly" , "Illegal arms dealer" .)