Energy required in pitch and run (4)
I believe the answer is:
tear
'run' is the definition.
(thesaurus)
'energy required in pitch' is the wordplay.
'energy' becomes 'e' (physics symbol as in E=mc2).
'required in' indicates putting letters inside.
'pitch' becomes 'tar' ('tar' can be a synonym of 'pitch').
'e' inserted inside 'tar' is 'TEAR'.
'and' is the link.
(Other definitions for tear that I've seen before include "Small flaw, as in glass" , "Rend; travel in haste" , "Rip, pull apart" , "Move quickly; pull apart" , "Drop secreted by the lacrimal glands" .)