Someone said earlier that watching the video made them more understanding of the cashier's actions, but for me all the video really showed was just how he really did take it too far - I kept expecting him to stop every time there was a long pause. Reading the story I was completely sympathetic to the cashier, and I still am a whole lot more sympathetic to him than to the customers, but I think the consensus is right that he went too far.
We can't see the women in the video, so I suppose we can't be completely informed on whether or not he had any possible reason to continue, as there was some debate about earlier. But most of the evidence suggests to me that it was no longer necessary self defence at all, and it was just blind rage making him continue to hit someone that was already down. As long as the girls were on the ground, which they appeared to be, the only reason to continue to attack them is if they were getting to their feet very quickly and seemed to still be very aggressive, which didn't appear to be the case given the time between the hits, or if they were reaching for a gun or maybe a knife - and I assume if they had been armed it would have been reported in the story. So while I suppose there is a possibility that it could still be considered self defence, it seems pretty unlikely. Once they were down on the ground he could have backed away even further - he would still have had the pipe if they did come back for him.
Having said that, even though he's in the wrong, I still think what happened is pretty understandable. He obviously had trouble controlling his anger, but it's not his fault he was put in a position where he would have to. He wasn't going out looking for a fight which he would end up taking too far, he was just working and those customers put him in a position where he had to defend himself, and then adrenaline, rage, whatever kicked in and he went too far. He should face the consequences for that, but ultimately the blame still lies with those customers.
And to people saying that he should not have defended himself at all, I completely disagree. He was just doing his job, and the customers weren't just "getting beligerent" any more, they physically attacked him. He shoved them off him and ran away into the back of the restaurant, out of the conflict, where the customers shouldn't be able to go, and they then jumped over the counter and ran after him. What other reason would they have for doing that if not to attempt to cause him further physical harm? If they were going to "cool down" if the cashier backed away, it seemed like him running away into the back of the restaurant would be the time they would do it. It seems like if the whole restaurant was "willing to defend him if there was any sign of danger", now would be the time to do it. And it strikes me as the type of area where people who are prepared to get aggressive in a situation like that could easily be carrying a knife, or even worse. So I completely understand his decision to defend himself, and while I absolutely don't agree with continuing to hit people in the head when (as far as I can tell) they were no longer a threat (as that seems like a good way to kill someone), I do kind of understand how he ended up doing it.