Nasty footballer Cahill starts eating in the interval (8)
I believe the answer is:
meantime
'interval' is the definition.
(I know that meantime is a type of interval)
'nasty footballer' is the wordplay.
'nasty' becomes 'mean' (similar in meaning).
'footballer' becomes 'time' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'mean'+'time'='MEANTIME'
'cahill starts eating in the' is the link.
This may not be right. Some or all of it may be part of another bit of the clue.
Can you help me to learn more?
(Other definitions for meantime that I've seen before include "For the moment" , "Intervening period" , "interval" , "interim?" .)