Energy cuts must stop (5,2)
I believe the answer is:
heave to
'stop' is the definition.
(I've seen this before)
'energy cuts must' is the wordplay.
'energy' becomes 'e' (physics symbol as in E=mc2).
'cuts' means one lot of letters goes inside another (some letters cut their way into other letters).
'must' becomes 'have to' (I've seen this before).
'e' going within 'haveto' is 'HEAVE TO'.
(Other definitions for heave to that I've seen before include "Of ship, stop without anchoring or mooring" , "(Of a sailing vessel) stop moving" , "come to a stop for navy" , "stop at sea" .)