I think the biggest incident was the near race war we had at my high school.
One Friday night, during the school year, a student (we will call him Tim) attempted to buy pot off of a friend. (we call that friend Mike). Mike was black and he went to a school that only had about 30 black students out of all the grades. Outside of school Mike hung out with mostly other black kids who didn't attend the school, but lived in the neighboring areas.
To keep the story short, Tim got ripped off when attempting to buy pot from Mike's friends. Tim gathered a couple of a friends to try and demand his money back, but Mike's friends (who vastly outnumbered Tim's 2 friends) weren't having any of it. They ended up beating the absolute shit out of Tim and his 2 friends. Tim ended up in the hospital needing brain surgery because of the repeated hits to the head with a brick. One of Tim's friend's face was smashed in with a 2x4 and needed plastic surgery to fix his nose and the third friend only got punched a couple times before fleeing on foot to call 911 as he saw Tim appear to be dead.
It was a disaster, but it didn't end there. When Tim's large group of friends from school found out what happened they attempted to track down those who nearly (and at this point still possibly) violently killed their friend in large swarms.
The thing was, Tim mostly hung out with white kids and Mike mostly hung out with black kids. So it was clear whose side everyone was on.
Tim's many friends managed to surround one of the black kids homes, but the police were called and were able to defuse the situation before violence ensued.
The next Monday in school, it was absolute insanity. Due to fear of retribution, Mike enlisted his many black friends to come to the school for the opening bell to help have his (and his friends who helped nearly kill Tim) 'back.'
I remember that morning, people were freaking out, there were so many students who didn't attend the school walking through the halls. Some of them fairly old (mid 20s) and very large black kids. You could sense that there was something big about to go down.
Luckily the administrators got a hold of the situation (with the help of the police) to get the non-students out of the school and keep Tim's friends from harming Mike or his friends.
In the end Mike and a couple of his friends went to juvenile detention and possibly some real jail; but I can not recall with what charges. Tim ended up surviving the vicious beating, but was never the same and ended up committing suicide some years later.
The whole situation was pretty tragic. That's the short version, the long version is much more incredibly detailed but I didn't want to take up any more space.