My reason for being in league to begin with (9)
I believe the answer is:
initially
'to begin with' is the definition.
(I've seen this before)
'my reason for being in league' is the wordplay.
I cannot really understand how this works, but
'in' is found in the answer.
'league' could be 'l' (abbreviation) and 'l' is present in the answer.
This may be the basis of clue (or it may be nonsense).
Can you help me to learn more?
(Other definitions for initially that I've seen before include "Firstly" , "To begin with" , "How laser, for example, was put together" , "At the start" , "In the beginning" .)