Hummers are tanking up to keep up their fat. Just to hover while eating takes many calories. Aggression is common at feeders because when food starts getting scarce, hummingbirds get the scarcity mentality. They are hypervigilant and territorial, which takes a lot of calories.
"We're still having about 50 hungry hummers busy at the feeders. Sometimes they all sit calmly together on a feeder and eat. Other times war breaks out. The image shows both."
Kenneth Drake in Willis, Texas (September 29, 2013)