Two soldiers among Liverpool fans perhaps must be stars (3,6)
I believe the answer is:
red giants
'stars' is the definition.
(type of star)
'two soldiers among liverpool fans perhaps' is the wordplay.
'two soldiers' means two substitutions for 'soldier'.
'soldier' becomes 'GI' (GI can mean a US soldier).
'soldier' becomes 'ant' (soldier is a type of ant).
'among' indicates putting letters inside.
'liverpool fans perhaps' becomes 'Reds' (nickname for Liverpool FC).
'gi'+'ant'='giant'
'giant' going into 'reds' is 'RED GIANTS'.
'must be' acts as a link.
(Other definitions for red giants that I've seen before include "Stars of high luminosity" , "Very large stars" .)