Becomes hard to follow case of Etonian political theorist (6)
I believe the answer is:
engels
'political theorist' is the definition.
(I've seen this before)
'becomes hard to follow case of etonian' is the wordplay.
'becomes hard' becomes 'gels' (I can't justify this - if you can you should give a lot more credence to this answer).
'to follow' says to put letters next to each other.
'case of' suggests removing the centre (outsides of).
'etonian' with its centre taken out is 'en'.
'gels' after 'en' is 'ENGELS'.
Can you help me to learn more?
(Other definitions for engels that I've seen before include "Early socialist" , "Communism's co-founder with Marx" , "Marx's patron" , "Early Communist philosopher" , "Co-author of Karl Marx" .)