Guy filled with energy left kid (6)
I believe the answer is:
delude
'kid' is the definition.
(I've seen this before)
'guy filled with energy left' is the wordplay.
I cannot really understand how this works, but
'energy' could be 'e' (physics symbol as in E=mc2) and 'e' is found in the answer.
'left' could be 'l' (common abbreviation) and 'l' is present in the answer.
'guy' could be 'dude' (both can informally mean a man) and 'dude' is found in the remaining letters.
No letters remain.
This explanation may well be incorrect...
Can you help me to learn more?
(Other definitions for delude that I've seen before include "Mislead; deceive" , "swindle" , "Mislead or fool" , "Cause to believe something untrue, deceive" , "Deceive, lead on" .)