Female Black Chinned Perhaps?
This little hummer had a busy evening buzzing over my backyard 3 times while chasing off a larger bird, or being chased by a larger bird, sometimes it was hard to tell. I could hear he/she humming long before I could see them. It came to the feeder twice in thirty minutes, time out from battle I guess. I had forgotten how fast and noisy they are. Not the best picture, I never could see the throat, but I think it was a female Black Chinned. Any other guesses.