Numbers take charge in stress (7)
I believe the answer is:
tension
'stress' is the definition.
(I know that stress can be written as tension)
'numbers take charge' is the wordplay.
'numbers' becomes 'tens' (ten is a kind of number).
'take' is a charade indicator (letters next to each other).
'charge' becomes 'ion' (an ion is a charged particle).
'tens'+'ion'='TENSION'
'in' is the link.
(Other definitions for tension that I've seen before include "State of strain or suspense" , "Strain, nervousness" , "A pulling strain" , "Conflict" , "Intones (anag) - stress" .)