What is In Play?
A stock is in play when it is widely believed to be a takeover target.
How Does In Play Work?
Let's say Company XYZ has a ton of cash on its balance sheet, and activist investors have been pressuring it for nine months to sell. Company XYZ finally decides that it is for sale, and announces that it is exploring 'strategic partnerships' with interested investors.
Company XYZ stock is in play.
Why Does In Play Matter?
When a stock is in play, it can run up quickly. That's because the eventual buyer is likely to pay a premium over the current stock price in order to induce the shareholders to sell the company and to beat out any competing bidders. For that reason, some traders are interested in stocks that are in play, and perhaps more important, stocks that could become in play soon.