I had a home raised replacment heifer that was calm as could be. One day she was fine the next I walked to the gate on a 20 acre pasture of which the cows were practically out of sight. She came on a full charge from over the horizon blowing snot and hollering and much to my surprise she wasnt bluffing. She rolled me a few times on my way to and over the gate. Not sure what happened in 24 hours but she never did calm down.
I had a Brahman cross cow suddenly charge me when I was walking in the pasture with my children, who were small at the time. I picked my daughter up and stepped in front of my son, and when she got about 8' from us I yelled real loud and she went past us instead of over the top of us. When we crawled through the fence into an adjoining pasture I don't mind admitting I had to sit down for a minute.
She had a small calf, but that wasn't her first, she had never been aggressive before, and we weren't anywhere close to her or the calf when she charged, so I don't know what happened. A few days later my father and I went to pen the cattle and sell her and the calf and she didn't want to let us out of the truck. Luckily, at one point she went on one side of the truck and her calf was on the other, so I jumped out, grabbed the calf, jumped in the trailer, and closed the door behind me.
She was circling the trailer and snorting, wanting to get to me and the calf. I closed the calf up in the front of the trailer, climbed up on top, and managed to open the back gate. She ran inside, and I closed it and climbed back down.
That was at least 25 years ago, but I have still never been so glad to see the trailer door closed on an animal.