1.
If someone is knocked down or is knocked over by a vehicle or its driver, they are hit by a car and fall to the ground, and are often injured or killed.
He died in hospital after being knocked down by a car...
A drunk driver knocked down and killed two girls...
A car knocked him over.
= run over
PHRASAL VERB : be V-ed P , V P n (not pron) , V n P
2.
To knock down a building or part of a building means to demolish it.
Why doesn’t he just knock the wall down?...
They have since knocked down the shack.
= pull down
PHRASAL VERB : V n P , V P n (not pron)
3.
To knock down a price or amount means to decrease it. ( mainly AM; in BRIT, usually use bring down )
The market might abandon the stock, and knock down its price...
It manages to knock rents down to $1 per square foot.
PHRASAL VERB : V P n (not pron) , V n P