Clue: Act of authorising goal line technology, init­ially, is complex (12)
Answer: LEGALISATION
Explanation: Definition: Act of authorising
(goal line **t** is)*, with the initial from **t**[echnology] – but this is missing a second '**a**' and would give 'legislation' but not LEGALISATION…
 is "initially" also meant to apply to **a**[uthorisaton]?