Outcome of increased effort (6)
I believe the answer is:
upshot
'outcome' is the definition.
(synonyms)
'increased effort' is the wordplay.
'increased' becomes 'up'.
'effort' becomes 'shot' (both can mean an attempt).
'up'+'shot'='UPSHOT'
'of' acts as a link.
(Other definitions for upshot that I've seen before include "Event" , "anti-aircraft fire?" , "Outcome, final result" , "Outcome of vertical discharge?" , "issue" .)