Flexibility means going after fish from the east (6)
I believe the answer is:
leeway
'flexibility' is the definition.
(I've seen this before)
'means going after fish from the east' is the wordplay.
'means' becomes 'way' (a way or means of doing something).
'going after' says to put letters next to each other.
'fish' becomes 'eel' (eel is a type of fish).
'from the east' says the letters should be written backwards (on a map from right to left).
'eel' back-to-front is 'lee'.
'way' put after 'lee' is 'LEEWAY'.
(Other definitions for leeway that I've seen before include "Margin, latitude, room" , "Slack" , "Limited room for manoeuvre" , "Flexibility" , "play" .)