Throw a coin from a height, it come down - and come to be rotated. why?

When the coin touches ground, this is still in motion and hence rotating.

newtons law of motion: what stays in motion will remains so until external force is added to it. here the ext force is the ground that stops it hence it starts rotating on its round circumference.

i feel i remember the physics lectures i studied ...lol

The explanation by Pearls Leo is correct. The coin was in motion and external force namely ground stopped this. But the coin will not abruptly stop and hence rotates.

People who live in glass houses shouldn't throw stones.

It is a law of science which applies to the coin thrown from a height.