I have had my main flock rooster turn on me before. If you understand roosters, and have a good rooster, you can probably figure why they occasionally act aggressively.
Example: my Speckled Sussex rooster spurred me (random) one night when I had a whole big bowl of feed, it spilled everywhere & he spurred me good. Next night, same thing. I put him in a dog crate to "reset" his attitude. One week of reset time worked wonders. In the end I determined he spurred me because we had just set our clocks forward an hour (daylight savings time) therefore in his mind, I was putting them up a whole hour earlier than I should have.
I've also had a very beautiful Rhode Island Red cockerel. He was so mean and aggressive I absolutely knew he was not going to be able to acclimate to the flock.