play the market
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.
The American Heritage® Idioms Dictionary Copyright © 2002, 2001, 1995 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company.