Having spent many years in a school uniform, if kids are determined enough they can pull down even properly fitting pants. It leaves some serious scrapes and even bruises though. If the pants are too tight the student might have left them unbuttoned, which would make them quite easy to pull down. While that might be the case, or the student might just have been out of the dress code, I fear that you will cause more problems by pointing this out.
IF the pants fit properly and your son pulled them down then they may up the charges to assault of some kind.
If the pants didn't fit right or were improper for the dress code, it sounds as if you are trying to switch the blame away from your son.
The school and the court will say that what the other boy was wearing was not the problem and has no bearing on your problem. Or they will say the boy was within the dress code and your son hurt him. You do NOT want this, of course.
It would be best, in court, to not bring this up, in my opinion. If the court and school think you are trying to switch the blame away from your son and onto his victim (the other kid is a victim in the eyesof the school and the court, most likely.), then the school and court will start to blame his problems on you. They will blame you because you try to keep your son from being responsible for his actions. They will latch on to this and everything else you have done, or will do, will all be looked at through the lens of "she says it is always someone else's fault".
It is dumb and idiotic of the school to be so narrowly focused, but they usually are. Especially once something has gone to the level where the court is involved.
Do you think your son needs an attorney? An attorney might be able to bring this up without the problems that will come up if you bring it up.
Or the lawyer will know that it won't be considered relevant in this hearing.
It really does sound like the new liason officer is trying to assert authority however he can. He probably feels very insecure, esp if he looks close in age to the students.
Sadly, our difficult children have mouths that escalate everything they are involved in to new levels. This time it is to a new level of bad. HOpefully he will be able to control himself during the hearing.
If you have questions about if attorneys are recommended or whatever, call the court clerk. It also might help if you had the judge's name and the clerk would be the person to ask about that also.
Good luck. I am sorry this all got so overblown. But you know how your difficult child's mouth makes you crazy. Imagine how it looks to a new officer who isn't very confident in his position and abilities (as yours sounds like). I can see how the constant challenges and jeers could make the officer keep taking it to the next level. A more seasoned officer could have handled it differently, but everyone has to start learning somewhere.
Gentle hugs,