Average guy, limiting energy (4)
I believe the answer is:
mean
'average' is the definition.
(type of average)
'guy limiting energy' is the wordplay.
'guy' becomes 'man' (guy can informally mean a man).
'limiting' means one lot of letters goes inside another.
'energy' becomes 'e' (physics symbol as in E=mca).
'man' placed around 'e' is 'MEAN'.
(Other definitions for mean that I've seen before include "show" , "Bad-tempered" , "Intend; unkind" , "of little value" , "Signify; stingy" .)