I had no idea those hyenas were so big.
I saw one of those Lions vs. Hyena shows on Discovery Channel once, where they were fighting over a kill and it was pretty evenly matched (like 10 lionesses to 20 hyenas). There was a lot of posturing, as the lionesses tried to scare off the hyenas and they tried to intimidate the lionesses. The fight went on for a while, and one of the lions was critically wounded.
Suddenly, all the lionesses just ran like hell, and all these hyenas were standing around looking like champs. Then, out of the bushes, a single male lion came up. Within seconds, he had killed two of the hyenas and was moving towards a third one. Despite the fact that he was outnumbered like 18-1, the hyenas wanted no part of him. They ran like hell, and the male lion was left alone with the carcass of the buffalo (or whatever it was).
They explained that the male lion has so much testoterone, that when he gets pissed he will kill any and everything in his AO until he is, himself dead. That's why the female lions took off, they knew the cavalry was coming.
The other striking part was that the male lion didn't roar or posture at all. He just ran silently up and started killing things. It was a pretty impressive show, made even more so by seeing the size of that hyena in the above picture.