Score at the wrong end (3,4)
I believe the answer is:
own goal
'score at the wrong end' is the definition.
(I've seen this before)
This is all the clue.
(Other definitions for own goal that I've seen before include "bad mistake" , "Goon law (anag.)" , "Self-inflicted wound" , "A self-inflicted injury, from soccer" , "Defender's faux pas" .)