There is, it auto opens the blizz launcher, then loads the game. You can go through the file where the game is located, find the icon without the phrase "launcher" next to it and the game will load, but then right before logging in, will stop and a warning will flash and say you need to open Battle.net app to run the game. There was a link to an older forum with instruction on how to play without the blizzard launcher however it was flagged and removed for going against code of conduct. Which only tells me that there must be some sort of agreement or the method in order to accomplish opening the game without the launcher is "forbidden"