Ounce for ounce Hummers are one of the most vicious birds on earth.
Last year I had to literally separate two of them.
They were fighting, and one flew into the door. When it hit the ground, the other one jumped right on it...right on the ground. I ran outside and scooped them both up before the cat saw them. I had to pull the one off the other one and then turn it loose. While I still had the addled one in my hand, the other one came right back and started fighting with it...while I was still holding it. I sheltered it from the mean one for a few seconds so it could get it's senses back, then it flew off...and started fighting again.
When I am working in the area where all the hummingbird feeders are, I get hit in the head quite often by them as they are fighting.
Weird little creatures.....