His hand knocked against the glass.
We got frightened when somebody knocked at our door late at night.
He was knocked down by a speeding truck.
That store has knocked down its prices.
He was knocked down by a car.
He knocked him down.
The speeding car knocked me down.
He knocked at every door for help.
Scarcely had I gone to sleep when somebody knocked at the door.
As soon as I lay on bed, somebody knocked at the door.
Someone had knocked him unconscious.
He was sleeping when I knocked at his door.