According to one version of this story, it was Zeus who caused Pallas' death by being a bit too overprotective against Athena. But then Pallas is of course older than in my version and I actually think they had gotten into a dispute and were fighting for real. When Zeus saw that Pallas was about to hit Athena, he held out the aegis and diverted Pallas' attention. He had nothing to do with it in my version, obviously.
... and that's why you better train with wooden swords.