Athlete finished second (6-2)
I believe the answer is:
runner-up
'second' is the definition.
(I've seen this before)
'athlete finished' is the subsidiary indication.
'athlete' becomes 'runner' (runner is a kind of athlete).
'finished' becomes 'up' ('up' can be similar in meaning to 'finished').
'runner'+'up'='runnerup'
(Other definitions for runner-up that I've seen before include "Contestant in second place" , "One who is second in a race" , "Second best?" , "Second-place" , "One nearly winning" .)