The best penalties finish in net (6)
I believe the answer is:
finest
'the best' is the definition.
(the most excellent or fine)
'penalties finish in net' is the wordplay.
'penalties' becomes 'fines' (fine is a kind of penalty).
'finish in' indicates one should take the final letters.
The final letter of 'net' is 't'.
'fines'+'t'='FINEST'
(Other definitions for finest that I've seen before include "Most exquisite" , "Of the highest quality" , "Most delicate or topmost" , "A1" , "Infest with the best" .)