Over his head, over the ground

I knocked him over his head so strong that he fell over the ground.

Is this sentence correct? [I mean the `bold-highlighed over' is (on the top of), and `violet-coloured over' is upon the surface of and not `fell over' which is a phrasal verb.]

Please help me.

Mister Micawber wrote:

No. I knocked him over the head so hard that he fell to the ground.

Thank you Mister Micawber.

From the dictionary. com

 [I applied the above meaning in my sentence, so I wrote (over the ground) to mean (upon/on the grond).]

I know I am wrong, but I don't know the reason for that.

Is there any reason which makes `over the ground' useless in my context?

Mister Micawber wrote:

Blame the dictionary-- it is difficult to make fully clear the meanings of many function words like prepositions.  Here, with 'over', the falling object must substantially cover the object upon which it falls-- the ground is much, much bigger than your friend's body, so 'over' does not work.

Thank you Mister Micabwer for giving such a nice explanation.