Playing cards in runs? That’s not right (4)
I believe the answer is:
aces
'playing cards' is the definition.
(ace is a kind of playing card)
'runs? that's not right' is the wordplay.
'runs?' becomes 'races' ('race' can be a synonym of 'run').
'that's not' is a deletion indicator (that has not).
'right' becomes 'r' (common abbreviation).
'races' with 'r' taken away is 'ACES'.
'in' acts as a link.
(Other definitions for aces that I've seen before include "Two will make deuce" , "Playing cards with single pips on their faces" , "Experts (in their field)" , "excellent service" , "Ones or elevens in cards" .)