Faulty shot having impact at first in film (6)
I believe the answer is:
mishit
'faulty shot' is the definition.
(shot hit in the wrong direction)
'having impact at first in film' is the wordplay.
'at first' indicates taking the first letters.
'in' indicates putting letters inside.
'film' becomes 'mist' (to film over is to mist or fog over).
The initial letters of 'having impact' is 'hi'.
'hi' inserted inside 'mist' is 'MISHIT'.
(Other definitions for mishit that I've seen before include "Strike (a ball) badly" , "Strike a ball so that it goes in the wrong direction" , "Poorly executed strike" , "shank?" .)