It's not just the tournaments, although having many players in a small area could be part of the problem IDK. But random client crashes can happen anywhere, I've noticed it usually does happen when you are doing a lot of switches, and fast. Like the client can't keep up with the player's requests and is just overloaded so it fails. I'd compare it to, for instance, imagine you open a folder in your computer which contains 100 files. Now if you open these files one at a time, no problem. But if you highlight them all and press enter, thereby attempting to open all at once, depending on your computing power, and file sizes, that level of input is likely to slow down and then crash your PC. That's how I can best describe what I THINK is happening here. I may be wrong
Has happened to me in the past. However, for future reference, in case you wasn't aware, the Rune pouch has an easy right-click option where you can select barrage, and there is a universal altar in the waiting room to change spellbook.