Rooster attack - will it happen again?

[Folly's place]

He does look evil!
Mary

 

[Shadrach]

My daughters watched my Wyandotte rooster “rip the back off” an Orpington hen. They have lots of space and rooster is about one year old. The rooster has always basically left the Orpington hens alone, the Orpington were here first and are 2yo. Will my rooster do this again? What may have caused this sudden attack. He doesn’t even mate with the orpingtons, it’s like I have two flicks. He’s also recently started chasing one of my daughters who’s 11.

What exactly do you mean by rip the back off?
You can't chase someone who doesn't flee in front of you.
The above points aside, in order to manage the cockerels behaviour one needs to know what has caused it. I assume that for a time your daughter hasn't had any problems with this cockerel before.
It is true that around this age a cockerels behaviour changes. All those who keep roosters will tell you as much. If one wishes to keep males then the transition from semi pet to a rooster is something one has to learn to deal with. I can't say all males at this stage are difficult, but ime most are to some extent.
If this is your first rooster then there are things you need to learn. It may be that learning process means you can't keep roosters. That's a promising start. If his behaviour and your families reaction to it are producing aggressive behaviour that may endager people then he has to go.
People post "into the crock pot with him" believing they're funny. It isn't funny. The probability is this rooster will be killed because he is acting like a rooster, nothing more.
I would ask you not to beleive those who trot out the tite expression "why keep a bad one when there are so many good ones out there" and get another male hoping for a different outcome. You will find through research and from talking to those with years of rooster experience that more often than not it is the keeper who causes aggressive behaviour in roosters.