1
general::
Phrase(s): play the (stock) market
to invest in the stock market. (As if it were a game or as if it were gambling.) • Would you rather put your money in the bank or play the market? • I’ve learned my lesson playing the market. I lost a fortune.
McGrawhill's American Idioms And Phrasal Verbs
2
general::
Trade in securities in order to make money, as in He is always playing the market with only mixed results. This term uses play in the sense of "gamble," a usage dating from about 1500.
American Heritage Idioms