Loop around sudden source of energy (5,3)
I believe the answer is:
crude oil
'source of energy' is the definition.
'crude oil' can be an answer for 'source' (I have seen 'Source of fuel' mean 'crude oil' so perhaps 'source' could also mean 'crude oil'). I'm not certain of the 'of energy' bit.
'loop around sudden' is the wordplay.
'loop' becomes 'coil' (synonyms).
'around' is an insertion indicator.
'sudden' becomes 'rude' (I can't explain this - if you can you should give a lot more credence to this answer).
'coil' placed around 'rude' is 'CRUDE OIL'.
Can you help me to learn more?
(Other definitions for crude oil that I've seen before include "output from rig" , "Unrefined petroleum" , "that has boring producers?" , "liquid asset" , "From which petrol is made" .)