my brother's 13 and he beat up this other kid today and I dont really know why. Apparently he punched and kneed him in the face.
The other guy was apparently "mouthing off" to my brother, so my brother beat him up, pretty badly so im told, then ran off.
The thing is, the guy he beat up is half his size, and I think he has behavioural problems or something like that, so my brother's pretty much a dick for hitting him.
Im not happy with him. What should I do ?

Thanks agony aunt.
Name and location withheld.