We finish last when it's muddy (3)
I believe the answer is:
wet
'it's muddy' is the definition.
(similar in meaning)
'we finish last' is the wordplay.
'finish' says to take the final letters.
The final letter of 'last' is 't'.
'we'+'t'='WET'
'when' is the link.
(Other definitions for wet that I've seen before include "Saturated; rainy" , "Moderately Conservative" , "Moistened" , "Saturated with liquid" , "Watery" .)