Decision affecting lawful position of striker? (7)

I believe the answer is:

offside

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'position of striker?' is the definition.
'offside' can be an answer for 'position' (I have seen 'Illegal position' mean 'offside' so perhaps 'position' could also mean 'offside'). I'm not sure about the 'of striker?' bit.

I cannot understand how the remainder of the clue works.

Can you help me to learn more?

(Other definitions for offside that I've seen before include "Dies off in illegal soccer position" , "In a position where ball can't be played (football)" , "in no position to score goal" , "Dies off (anag.)" , "Illegal football position between the ball and opponents' goal" .)

I've seen this clue in The Telegraph.

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