IDIOM ►
like a sitting duck
Meaning 1 ►▼
as a duck sits on water
Sentence 1
That target practice was easy, like hitting a sitting duck.
Meaning 2 ►▼
to be unaware of something about to happen
Sentence 2
The ememy's troops were like sitting ducks. They did not suspect an attack.
Derivation
A sitting duck is easier to shoot than one that is flying. A stationary target is easier to hit than a moving one.