Exploited by tennis player Chuck, given vaccination? (4,4)
I believe the answer is:
drop shot
'exploited by tennis player' is the definition.
(tennis term)
'chuck given vaccination?' is the wordplay.
'chuck' becomes 'drop' (drop can mean to chuck away).
'given' is a charade indicator (letters next to each other).
'vaccination?' becomes 'shot' (shot can mean a vaccination).
'drop'+'shot'='DROP-SHOT'
(Other definitions for drop shot that I've seen before include "One may land in court" , "Hit (in tennis, squash) awkward to return" , "strong highball? Hardly" , "Stroke" .)