Flounder perhaps in first half, somehow striker's finish missed (8)
I believe the answer is:
flatfish
'flounder perhaps' is the definition.
(flounder is a kind of flatfish)
I don't understand the remainder of the clue.
(Other definitions for flatfish that I've seen before include "Sole, plaice etc" , "Plaice or sole, for example" , "Swimmer" , "could be a fluke" , "Perhaps sole" .)