How about tracking corporate jets to buy stock in companies before a merger / acquisition. That blew me away when I first read about it.
[0] https://www.bloomberg.com/news/articles/2017-01-27/hedge-fun...
[0] https://www.bloomberg.com/news/articles/2017-01-27/hedge-fun...
He follows him to a private jet and finds out it's flying to mid-sized city that happens to be the corporate headquarters of a particular company. In the movie it's sort of implied that this activity is illegal.
I wonder if it actually was, and if so, why that would be different than what those hedge fund guys you reference were doing?