Deviate from course turning inside to obtain plan of action (8)
I believe the answer is:
strategy
'plan of action' is the definition.
(strategy is a kind of plan of action)
'deviate from course turning inside' is the wordplay.
'deviate from course' becomes 'stray' (stray off course).
'turning' becomes 'teg' (I can't explain this - if you can you should believe this answer much more).
'inside' means one lot of letters goes inside another.
'stray' going around 'teg' is 'STRATEGY'.
'to obtain' is the link.
(Other definitions for strategy that I've seen before include "Planning and direction of campaign" , "Get satyr to formulate tactics" , "Scheme" , "Plan or policy to achieve something" , "Overall plan for campaign" .)