Kick supporter: that's illegal (7)
I believe the answer is:
bootleg
'illegal' is the definition.
(similar in meaning)
'kick supporter' is the wordplay.
'kick' becomes 'boot' (booting is a kind of kicking).
'supporter' becomes 'leg' (I've seen this in another clue).
'boot'+'leg'='BOOTLEG'
'that's' is the link.
(Other definitions for bootleg that I've seen before include "Sell illicit alcohol" , "Illegally made recordings" , "Illegal product" , "Deal in illicit alcohol" , "Smuggle liquor" .)