Got a few;
Pompey store in 1992, a teenage lad was stabbed in the gut. not game related violence but by an anonymous stranger that was never caught. Police called, store closed for a week. did not see it happen personally.
Same store (hell, they are all gonna be from the pompey store), lad was beaten badly by another gamer. was thought that it was game related (the beaten lad is a famously bad winner) turns out it was half him rubbing it in the guys face like a child and half a cheating girlfriend issue.
A personal fav of mine because it is a personal story of mine; A regular matlow fella who had been coming to the store for years fights me and my nurgle army. bad tempered, real short and always acting "popeye-like" with rolled up sleeves and always regaling his heroic navy service stories to anyone with ears. I am 6'6", 138KG and a weight lifter. i get into a fair amount of fights because i either have A; a face you just want to punch or B: Am always targeted for my height and musculature. regardless, i won the match after my daemon prince, swooped in and killed off his tooled up termies. He accused me of cheating, i asked him to tell me how/what i had cheated at and he just raged on the spot for a few seconds before launching my prized daemon prince (which i had spent many, many hours converting an inquisitor scaled brother Artemus from) into the wall. I have only lost my temper 4 times in my life and that was one of them. i was not going to have my "honour" questioned by a dwarfy, loud mouthed sailor and then my model smashed.
Im not proud of what i did, but im not sorry for my actions either. i rounded the table and headbutted him. cut my eyebrow and knocked him to the ground. i was great friends with the manager, Paul at the time, we picked him up, made him a cup of tea and i apologized to him, He apologized back and that was that. Solomon the Suffered, seventh son of Nurgle was rebuilt from new pieces and still leads my army today.