Some people use "play the market" to mean, "I make investment decisions, and purchase stocks". That's the conventional meaning. In this case, though, he's con

Some people use "play the market" to mean, "I make investment decisions, and purchase stocks". That's the conventional meaning. In this case, though, he's contrasting the "play" as in "fun" aspect. He doesn't do it for fun, and instead treats it as work: minimizing risk, etc. If I were "playing" this, I could do it with Fake Money and compare strategies over time, or invest pretend money to do all the same work. I don't think I'd be able to do it if gambling with real money.