Lions might have that ingrained king-of-the-beasts reputation, but we've seen enough brawls to know that hyenas can be worthy challengers. And any big cat that finds itself in a hyena fight with no backup is in big trouble.  
This amazing encounter was filmed just recently in South Africa's Londolozi Game Reserve, and the lone lioness was lucky to get away without more serious injuries. 

"Being the most dominant predator in these parts, [lions] tend to not have too much to worry about in terms of competition, but as is so often the case in the bush, you can just never guarantee when the tables will turn," writes Amy Attenborough over on the Londolozi blog.

Attenborough, along with a tracker guide, was out in search of another feline predator – a female Londolozi leopard – when a telltale sound in the distance told them drama was unfolding nearby. "Hyenas make a wide variety of sounds which differ depending on whether they've got food, if they're calling to each other, if they're in distress or if they're marking territory. The noise that we heard was the unmistakable, excitable sound of heckling," she says.

Homing in on the commotion, the pair arrived on the scene to find a group of some 20 hyenas surrounding the lioness, who was crouched defensively on the ground while her vocal adversaries circled. It wasn't long, however, before fighting flared up. "It took a while for the hyenas to build up the courage, but once one of them had rushed in and bitten her on the rump, the others descended," recalls Attenborough

With size and strength on her side, the big cat could deal with any attackers approaching head-on, but the hyenas moved in from all sides, forcing her into a desperate game of swivel-and-swipe.  

It took a well-timed dash for safety to finally escape the fray, but the determined hyenas quickly gave chase. "Hyenas, although slower than lions, have incredible stamina and it looked like they were going to catch her as she retreated," says Attenborough.

With few escape options at hand, the big cat finally found shelter in the branches of a tree. (Lions might not be the most accomplished climbers, but the behaviour isn't as rare as you'd think.)

Finally defeated, the gang of spotted pursuers circled the base of the tree for a while before eventually moving off. As for lioness, she sustained just a few minor gashes and a cut lip. 

"[This] was a reminder that sometimes even the most dominant predators and those at the top of the food chain can find themselves as the underdog," says Attenborough.