Important rising star oddly missing football (7)
I believe the answer is:
pivotal
'important' is the definition.
(similar in meaning)
'rising star oddly missing football' is the wordplay.
'rising' says the letters should be written in reverse (going up in a down clue).
'star' becomes 'vip'.
'oddly missing' indicates alternate letters.
The alternating letters of 'football' are 'otal'.
'vip' in reverse letter order is 'piv'.
'piv'+'otal'='PIVOTAL'
(Other definitions for pivotal that I've seen before include "Crucial, critical" , "Of crucial importance" , "Crucially important" , "Of central importance" , "Central - decisive" .)