Scowl in dreadful shot (7)
I believe the answer is:
grimace
'scowl' is the definition.
(thesaurus)
'dreadful shot' is the wordplay.
'dreadful' becomes 'grim' (I've seen this before).
'shot' becomes 'ace' (type of shot in tennis).
'grim'+'ace'='GRIMACE'
'in' is the link.
(Other definitions for grimace that I've seen before include "Frown" , "Pained expression" , "Dour" , "Ugly facial expression" , "Smirk" .)