I'm sorry to hear that Toby and Havoc have been fighting.
Maybe it was because of the smell of the other cat on you.
Milly hates our neighbor's black cat that shows up in our yard sometimes and will growl and hiss at it from the window and sometimes lash out at Izzy if she is close by.
Milly & Izzy also play fight while I'm getting their food ready but not to the point of hurting each other.
When Milly does get moody like that, I like to get out a fun toy like Da Bird and let them burn off their aggression on the toy instead of on each other.
Also taking them outside on a leash and harness sometimes helps them burn off some energy so they don't fight with each other.
I hope that Havoc is feeling ok and that he and Toby are getting along ok now.
Maybe Havoc is just living up to his name.