Dropping ball in front of goal (8)
I believe the answer is:
omission
'dropping' is the definition.
(I've seen this in another clue)
'ball in front of goal' is the wordplay.
'ball' becomes 'o' (O looks like a ball).
'in front of' means one lot of letters go next to another (some letters go in front of others).
'goal' becomes 'mission'.
'o'+'mission'='OMISSION'
(Other definitions for omission that I've seen before include "Act of leaving out" , "Something left out or neglected" , "cut?" , "Exclusion" , "task not done" .)