I am not a lawyer. But I have watched multiple lawyers speak about it in various youtube videos etc(I like listening to/watching law vlog type of things). I have also watched much of the videos of the incident as well, partly because it is often included in said law videos. I could try and find some of those old videos but much of my watching was right after the news broke of the incident so there was missing information/etc. As such the videos aren't exactly a good watch now if you want to understand the trial since they weren't about the trial and not all the information was fully available(in fact I can think of at least one video that the creator, a cop I think instead of a lawyer, had to address a previous video they made because they had misinformation in it due to the fact that they were reacting to current events and just didn't get it right the first time. A "Sorry guys, I was wrong. That wasn't the case, this is what really happened" type of deal). There were probably hundreds upon hundreds of hours of people in the law field reacting to the events that night. Though obviously I did not watch all of them. I don't have THAT much free time.
From the start this was considered a fairly solid self defense case by many lawyers and folks who understand self defense. Now lawyers mind you don't usually speak in absolutes, particularly when it comes to self defense since such cases can have so many unknown elements that you are often betting on a sympathetic jury as much as the facts of the case. However, the sheer amount of video evidence in this case made it one of the stronger claims that I at least have ever seen. There were some questions though.
The first was the illegal gun possession charge, even after reading the law in question many of the lawyers weren't sure how that one would play out. Many of them saw what looked to be a hole in the law concerning 17 years old that could potentially get him off, others meanwhile shook their heads at that argument thinking it was quite the reach. I saw at least one(this was a lawyer on forum trying to break everything down) saying that the law in question was a mess. It had been amended so many times by so many different groups of lawmakers over the years that it had gaps an elephant could walk through(that was my interpretation of their post anyways, but it was obvious they were not happy with the way the law was written). In the end the prosecution withdrew the charge after they were asked what the length of the rifle was. The law in question is CLEAR that a short barreled rifle is off limits, it is only the full length rifle that he could possibly have been carrying legally. As for the full length rifles. In general if the law isn't clear it should fall in favor of the defendant, which is how the judge ruled. The instructions that were going to go to jury was that the law allows for a full length rifle or shotgun, but not a short barreled weapon. And with that set of instructions there was no point in the charge since the weapon clearly didn't fall into the prohibited category. A lot of people have pointed out that this doesn't appear to be the intention of the law(I think I saw a memo/meeting/whatever you call it type thing that was supposedly dealing with the statute in question where it was clear that the lawmakers were looking to carve out exceptions for hunting and target shooting not general carry). However, the law having holes in how it is written is on the lawmakers. IF the intent was to bar general carry of even long guns then it needs to be revised and made clear. In a case where you have a law being unclear ruling on it in the way that is favorable to the defendant is actually the best practice(in my opinion anyways, but I do believe in a system that favors the defendant).
If you are curious this is the act that changed it from allowing general carry for full length rifles to something fairly close to its current rendition. https://docs.legis.wisconsin.gov/1991/related/acts/18. This way you can make your own call on what you think it says. Personally I am rather surprised he dodged that bullet and do not have a hard time believing the intent was a narrow exception and not a general open carry allowance, however, I have been playing SRW 30 and haven't been watching too many lawyer reactions to the trial itself. So maybe lawyers are more or less surprised than I am. At the time of the incident it seemed a lot more divided, but maybe after a year of digesting the statute it seemed more obvious?
The second question is on the gun's legality. Not the possession, but whether or not a straw purchase was involved. That to my knowledge is still winding its way through the court system. Rittenhouse's friend who bought the gun and was planning to give it to Rittenhouse when Rittenhouse was old enough to own it and allowed Rittenhouse to carry it on at least 1 occasion is still in the process of going to trial over a straw purchase charge. I am not sure if this could get Rittenhouse in trouble too if his friend is found guilty of making a straw purchase. But this is one of the questions that has yet to be answered. I REALLY don't know this type of law, it wasn't brought up, except maybe in passing as an offhand comment, in any of the law vlogs I watched and I am not even sure what exact statutes are in play, so I can't even read the laws and try and make my own interpretation. I do know parents do this type of thing where they buy their kid a gun when they are underage with the plan to gift it to them when they are old enough. In some cases exchanged for chores/good behavior/good grades or sometimes even money if the kid has a part time job and wants something that is either limited or on sale now that won't or may not be there when they are of age. In the meantime they are allowed by the parent to use it for target shooting and hunting. Theirs but not theirs. Not yet. The question is can a friend do this for you(also in Rittenhouse's case apparently he gave cash to his friend not chores/behavior/grades in exchange, that could very easily sink any defense that it was a gift)? Heck, maybe that practice I described is actually illegal and it just never gets charged since it doesn't usually make the headlines. I don't know. But I'll be interested to hear how that case goes.
The third question was on intent. IF the prosecution could prove that Rittenhouse planned this all out and went down there with the intent to incite someone to attack him so that he could shot them, then that would have tanked the self defense claim, or at least severely weakened it. The prosecution was not able to show this beyond a reasonable doubt. That was my take on it, and apparently the jury's take as well. This was basically the best shot the prosecution had for the murder charges and they couldn't deliver. And to be fair proving intent beyond a reasonable doubt when you don't have a confession is REALLY hard. So I didn't think they had much of a chance here from the very start. Though the kid probably regrets running his mouth in the past before the incident since that gave the prosecution some potential ammo. Though even if that bit of audio had been allowed I still wouldn't view it as beyond a reasonable doubt. Weakens the claim, but doesn't destroy it since the statement was generalized and not directed at the night at hand. Mostly it would act as character testimony and they do try to limit that. Yes you can argue it is related to the case, but in my opinion it should only be allowed if very narrowly related to the case not just generally related(if you argue hard enough you can stretch related pretty darn far, but obviously this is something folks will constantly debate and go back and forth on). You aren't judging whether they are a good person overall or whatever, you are merely judging the event in question. I am getting off topic, but people constantly bringing up criminal histories and the ilk when it doesn't narrowly relate to the case has been ticking me off, particularly when it is being done to vilify folks. Rosenbaum's, Huber's, and Grosskruetz's histories do not matter. Rittenhouse getting into a fight with a girl does not matter. What matters is the chain of events during the night in question. If you can't directly and narrowly link something to the event in question then it is out of bounds and shouldn't be brought in.
The fourth and final question was provocation. If you go up and punch someone and they punch you back you can't hit them again and claim self defense because you provoked the attack. So if they could show that Rittenhouse provoked the attack then it would greatly weaken his ability to claim self defense. There is only one problem with this. If you read the law it is very reasonable. I was honestly shocked at how robust Wisconsin's self-defense laws are. I had just assumed that legally speaking there would be plenty of ways someone could defend themselves but still be on the hook legally(namely in cases where you started the initial fight or had a hand in the start of the fight). That is not the case. Wisconsin's law is so impressive that it covers every ridiculous scenario I throw at it(though I am not a lawyer, an actual expert of the law might be able to come up with a hypothetical case that breaks it, but my layman's mind sees it as pretty solid and at least one of the vlogs I listened to at the time made mention of just how impressive Wisconsin's law is, 'one of most robust self defense laws in the country' or something along those lines also I recall hearing someone say something along the lines of 'if you are going to claim self defense, Wisconsin is the state to do it in'). It is actually well done. So much better written then that mess of a dangerous weapon for minors law which almost certainly let him get off the hook when a better written version of it wouldn't have. But I should get back on topic. In places with reasonable self defense laws, you do not permanently lose your right to self defense if you start the fight. Rather you are held to a much higher standard. You MUST attempt to escape and may ONLY use force when your escape options have been exhausted AND you fear for your life or that you will be seriously injured. The thing is. Rittenhouse was trying to disengage at every turn and only used force after being cornered/knocked down and never fired at someone who couldn't be considered a threat, and it is all caught on video so there is no question or debate on what happened in those pivotal moments. He makes the higher bar, so even if he provoked the instance he still had a self defense claim. That said if the prosecution managed to convince the jury that the Rittenhouse was the provocateur it would not have been good for Rittenhouse. As I said at the top these cases can rely on the Jury being sympathetic since it is a trial where you basically say yes I did that illegal thing but I had good reason to do so. As such if the jury is convinced you started it you are a less likely to convince them that you had a good reason to do it. So the provocation was important to answer since it could pivot the jury, after all if the Jury already thinks you are the aggressor they are more likely to disagree that you exhausted all attempts to get out of the situation. And convincing a hostile jury is a very bad place to be, even if you maybe still have a reasonable claim.
Some other things that could have changed is that there may have been other laws he could have been charged under. Reckless endangerment, etc. Successfully arguing self defense helps against much more than just murder, but a lesser charge may have stuck even so. This is, from my understanding, part of the reason why some lawyers were pretty sure the gun charge would stick. Since juries will sometimes split the difference. They don't want to let someone fully off, but they also don't think it is reasonable to lock a person away for life. So they convict on the lesser stuff, but let the bigger stuff go.
But yeah TL;DR - If you run someone down and corner them you are likely the baddie and your victim is likely to have a very strong self defense claim. Somewhat unrelated but it sounds like the Arbery case is heading toward the proper verdict as well. Kinda the opposite of Rittenhouse. In Rittenhouse's case there was only a narrow window for conviction, intention or possibly provocation making the jury unsympathetic. In Arbery's case there is only a very narrow window to avoid conviction and it sounds like the judge has slammed that window shut on the defense. So lots of good news at the end of this week regarding justice being served.
Edit- I didn't bring up all the controversies regarding the judge though I did read up on some of that even if I haven't been following the livestreams/law vlogs on the case, so I could go a bit into that if you wanted.