S.H.
From 9-12 years old, a child is a "Tween."
Preteen.
Google Search "Tween boy development."
I have a 9 year old girl.
Going to 5th grade.
Her teacher says, that from here on out, kids are becoming Tweens. It is hard. And sure, their hormones and physiology is changing too.
I have a friend with a son who is 9. And he gets surly too.
Perhaps, get him some books for boys, per Tween topics.
But for misbehavior, you gotta talk with him too.
In addition to whatever punishment you feel is appropriate.
BUT, for me... and my daughter, when she gets moody fits, I actually will in a calm voice tell her "I can tell you are not feeling great... come, lets go over here and talk..." And I let her, talk. Letting her tell me whatever she is feeling or what not. Sometimes she just "needs" to vent about things. Anything. Fine. I let her. Talking this way with her, creates a "bonding" with me... and her feeling safe in telling me things. I don't judge her. Because, I WANT her, as she gets older, to KNOW... that she can tell me things... happy things or grumpy things. And she trusts, me. Doing this with her, helps her to deflate. And then she feels better after.
It works. For her.
My late Dad used to say, that if a child cannot vent or talk to their parent at home about anything... then where will they go to do that??? And with whom? My late Dad, KNEW... (especially when we were Teens), that this was important. And HE was the person, we went to for talking about anything. Because, kids this age do NOT know how to deal with frustrations or issues or what not, instinctively. But they, even if they are antagonistic toward us, they need to have a soft place to fall, too. Because they are feeling out of sorts. So the parent, is very important... in this age spectrum.
And YES, he is responsible for his actions.
It is a choice.
With my daughter, we TELL her it is a CHOICE she makes.... on how to spout off her irks, or not. And we suggest... better ways in which she can let it all out.
How about you talk to your son??? In an open calm way... and see what he says, about why he is so incongruous, lately?
No matter how... irking a child can be... you need to find a way to "bond" with him. I find that it helps a great deal.