Decisive game’s influential, if boring (9)
![Ross](/clue/static/ross-mug.min.png)
I believe the answer is:
semifinal
But I can't explain it at all! Could you help me understand?
(Other definitions for semifinal that I've seen before include "Penultimate cup game" , "Tie" , "big match" , "Competitive match" , "big game" .)