Being negligent, I'm put back in the reserves before the start of the season (6)
I believe the answer is:
remiss
'being negligent' is the definition.
(similar in meaning)
'i'm put back in the reserves before the start of the season' is the wordplay.
'put back' says the letters should be written in reverse.
'in the' is an insertion indicator.
'reserves before' becomes 'res' (I can't explain this - if you can you should believe this answer much more).
'the start of' indicates taking the first letters.
The initial letter of 'season' is 's'.
'im' backwards is 'mi'.
'mi' inserted inside 'res' is 'remis'.
'remis'+'s'='REMISS'
Can you help me to learn more?
(Other definitions for remiss that I've seen before include "Neglectful" , "Derelict in duty" , "Negligent, slack" , "Lacking attention to duty" , "Negligent in performance of duty" .)