This very weird incident in Arena (1 versus 1)

I was playing in arena when the player I was up against dropped me from full to 1/4 in health. How does that happen?

Here are the clues:

1. Player still had weapon in his hands so not throwing his weapon.
2. He had claws and did not use special on me when the incident took place.
3. I had 13 ms.
4. He was very close to me when he dropped me to 1/4.
5. He used claws attack (normal).
6. He did not stagger me or make me fall down. 
7. I was ranked three arrows and the opponent has ranked two arrows.

My theory is that lag took place and freeze-ed my character while my opponent dropped me to 1/4. Still, I do not know exactly what happened but I highly suggest that this gets an immediate fix because this is game-breaking. I do not want to drop quickly just because of lag. I really despise this kind of gameplay and I don't want to see anymore of this. Everyday when I log on to play, all I see is lag, lag, lag, lag, lag and more lag. It's so common, that I don't even bat an eye when I see a player just moving in one direction for no apparent reason. This happens to me too and even at 13 ms, I don't like it at all. Keep in mind that I play primarily on North American server and I have 13 ms. What is this? Can you do anything about this? Honestly, no one wants to lose all their hard work to lag.