Imagine what you would do in this situation. You're a deer (I realize that's a reach) and you're being chased by a coyote. What do you do? If you're in Yellowstone National Park, you hide in a nearby bison herd which is exactly what just happened as a new video shows.
When you go hunting, you hope you'll run into a big buck. You also understand that seeing a mountain lion is a possibility. It's not common though to see both animals in a mortal battle which is what some Colorado hunters witnessed recently.