One watching old boy against McEnroe? (8)
I believe the answer is:
observer
'one watching' is the definition.
(I've seen this before)
'old boy against mcenroe?' is the wordplay.
'old boy' becomes 'ob' (abbreviation).
'against' says to put letters next to each other.
'mcenroe?' becomes 'server' (I can't explain this - if you can you should believe this answer much more).
'ob'+'server'='OBSERVER'
Can you help me to learn more?
(Other definitions for observer that I've seen before include "Newspaper - witness" , "Sunday newspaper" , "Looker-on" , "Spectator - or another weekly publication!" , "Someone watching" .)