At an individual level, likely impossible without a lot of capital.
At a company level, pretty darn easy. There is a lot of speculation that Coinbase just did it intentionally this past week. As soon as Coinbase launched support for Bitcoin Cash, the price of Bitcoin plummeted and the price of Bitcoin cash spiked dramatically as people moved money around. Some people have suggested that there was some insider trading going on at Coinbase when this happened, and that a lot of their employees profited dramatically from it.
At the end of the day thats all just conjecture right now as far as I know, but its still a lesson to be careful when investing into crypto.