Go wild? Sport has a monk going wild (3,4)
I believe the answer is:
run amok
'go wild?' is the definition.
(I've seen this in another clue)
'sport has a monk going wild' is the wordplay.
'sport' becomes 'ru' (rugby union).
'has' means one lot of letters go next to another.
'going wild' indicates anagramming the letters.
'a'+'monk'='amonk'
'amonk' with letters rearranged gives 'namok'.
'ru'+'namok'='RUN AMOK'
(Other definitions for run amok that I've seen before include "Go on frenzied, murderous spree" , "Go berserk" , "Rampage" , "go on killing spree" .)