Last year I volunteered for Yellowstone NP as a wildlife videographer (the government job title is a lot more detailed) and had an unforgettable experience recording aggressive elk behavior. This elk ran up a couple steps and chased us off from this "safe" viewing location in front of Mammoth Hotel. For the rest of the week I chose another location and was able good footage of him attacking as the tourists fled the deck. The most amazing memory is that several people would not leave, as if they owned the space, when it charged the deck. The entire week was an experience I will never forget.
Technical: slight blurring due to shooting over my shoulder as I was making a quick exit.