Season's opening practice has athlete madly keen (9,2,3,5)
I believe the answer is:
straining at the leash
'season's opening practice has athlete madly keen' is the definition.
I don't know anything about this answer so I can't tell whether this works.
'season's opening practice has athlete madly' is the wordplay.
'opening' suggests taking the first letters.
'practice' becomes 'training' (I am not sure about this - if you are sure you should believe this answer much more).
'madly' is an anagram indicator.
The first letter of 'seasons' is 's'.
'has'+'athlete'='hasathlete'
'hasathlete' with letters rearranged gives 'attheleash'.
's'+'training'+'attheleash'='STRAINING AT THE LEASH'
Can you help me to learn more?
(Another definition for straining at the leash that I've seen is " Raring to go".)