Checks energy releases (4,2)
I believe the answer is:
lets go
'releases' is the definition.
('let go' can be a synonym of 'release')
'checks energy' is the wordplay.
'checks' becomes 'lets' ('let' could historically mean an obstruction).
'energy' becomes 'go' (I've seen this in other clues).
'lets'+'go'='LETS GO'
(Other definitions for lets go that I've seen before include "Releases from one's grip" , "Order to leave" , "fires" , "Liberates" , "Come on then, we're off!" .)