This happens in every game, to be honest. Even when it's on local multiplayer.
My brother once unplugged my GameCube controller when I was about to win a race, for instance.
And, ragequits by JP gamers happen all the time in my corner of the Pokéworld.
I WON A BET AGAINST AZUREN! WOOOOOOOOOOAAAAAAAAHHHHHHHHHHHHHHHHHHH
:3