So you sign a non-compete, but if you ask you get told that things like games or open source contribution are fine.
Then you come in and you find out that internal policy is that you need approval for everything. That's not that unreasonable, and they are usually not too slow. for most things they don't have a blanket ban.
THen you don't quit immediately because you don't want to hand back your signing bonus, but once you it that one year mark it becomes an option and many people do quit at that point.