The African buffalo is a hulking 2000 lb beast, with massive sharp horns and a 2-inch thick tough hide. There are videos of African buffalo casually throwing aside lions that jump on them, or goring them to death. You can see here in this video ( https://www.youtube.com/watch?v=N9j3v01F5mU ) how much respect the lions give to a healthy young bull, unwilling to make the attacking move even when there are three of them. In this video ( https://www.youtube.com/watch?v=aZc0666cNF4 ), you see the entire fucking pride being too cowardly to jump on a single healthy prime bull.

Buffalo are not defenseless, the skin of adults is tough to break through even for lions, their horns are deadly sharp and their kicks are strong enough to break jaws or ribs of unlucky lions.

But they are hunted by lions anyway, because lions don't hunt buffalo alone, they hunt with their pride. And lions don't hunt adults, they hunt the young, the old, the sick and the lonely.

If the buffalo unite and fight back, lions would either go extinct, or at least disappear from areas inhabited by buffalo. Unfortunately, buffalo are just silly herbivores incapable of high-level critical thinking, unlike humans who have the most powerful brains on the planet.