Go into your 'My Documents' and find the Rocket League folder in there (not the steamapps folder). See what the file size of 'Launch.log' is. If it's huge, delete it and try to launch the game again.
For me, the path is Documents > My games > Rocket League > TAGame > Logs
Quelle:
https://www.google.com/url?sa=t&source=web&rct=j&url=https://amp.reddit.com/r/RocketLeague/comments/aelemr/rocket_league_wont_start/&ved=2ahUKEwj6juWxkO7rAhVMjqQKHVeqAMcQFjAAegQIBRAB&usg=AOvVaw1aSe1Xn55oYZSC7pacWuQe