If you have a better model for the outcome on a Sport than the bookmakers you can make money gambling against them. The reason this doesn't work in practice is that bookmakers will simply reduce your stake limits, to the point that it's a waste of time, if you beat them consistently.

There are fewer problems like this in the stock market. However, getting a better model than the players in the market is arguably more difficult. However, with the resources of Berkshire you can do things which a retail investor couldn't dream of, stuff like using satellite imagery to approximate performance. Or paying the CFOs latest squeeze for information (or at least the same but laundered through a 3rd party).