killer instinct

(idiomatic) The natural inclination to do whatever is necessary to succeed (including extreme violence)

Example: Used other than as an idiom: see killer,‎ instinct.
2011 January 25, Les Roopanarine, “Wigan 1 - 2 Aston Villa”[1], BBC:
  Not for the first time this season, that lack of killer instinct - combined with an approach more responsive than probing - proved costly for Martinez's men.