Kicking the attacker before they attempt to continue their attack would not be justified.

If an attacker keeps trying to get up and fight 9 times, the 10th kick would be justified.

Exactly, "trying to get up AND fight". But the latter part is absent in this video, just trying to get up is not indication of attempting to continue the attack. Getting up and moving towards the person? Maybe. But it is not possible to justify kicking someone trying to get up in any reasonable way under these circumstances.