Infectious game advanced with six in the lead (8)
I believe the answer is:
virulent
'infectious' is the definition.
(thesaurus)
'game advanced with six in the lead' is the wordplay.
'game' becomes 'RU' (rugby union).
'advanced' becomes 'lent' (advance can mean to lend).
'with' means one lot of letters go next to another.
'six in the lead' becomes 'vi' (I can't explain this - if you can you should believe this answer much more).
'ru'+'lent'='rulent'
'rulent' put after 'vi' is 'VIRULENT'.
Can you help me to learn more?
(Other definitions for virulent that I've seen before include "Violent or poisonous from a liver nut" , "Venomous" , "Highly poisonous" , "bitterly hostile" , "Actively poisonous" .)