Uncle out on a run — that's some sort of energy! (7)
I believe the answer is:
nuclear
'some sort of energy' is the definition.
(nuclear energy is a type of energy)
'uncle out on a run' is the wordplay.
'out' indicates anagramming the letters (out can mean wrong or inaccurate).
'on' means one lot of letters go next to another.
'run' becomes 'r' (cricket abbreviation).
'uncle' anagrammed gives 'nucle'.
'nucle'+'a'+'r'='NUCLEAR'
'that's' acts as a link.
(Other definitions for nuclear that I've seen before include "one's immediate family?" , "Concerning subatomic particles" , "An ulcer (anag)" , "Using atomic energy" , "Derived from fission or fusion" .)