What happened 

Shares of Boyd Gaming Corporation (BYD 0.86%) plunged 16.9% in May, according to data provided by S&P Global Market Intelligence, after a competitor reported disappointing results. Concerns about a potentially slowing U.S. economy couldn't have helped matters, either. 

So what 

Boyd Gaming reported earnings late in April and shares barely moved, but the Penn National Gaming (PENN 2.71%) results in early May sent a bit more of a shock through the gaming market. Penn's revenue was $1.28 billion, slightly below estimates, and earnings of $0.35 per share missed estimates by $0.02. 

Gaming table with gaming chips, dice, and playing cards.

Image source: Getty Images.

On the other hand, Boyd's results were in line with expectations, which is why the stock didn't move, but acquisitions made in the past year made estimates difficult to make. If we look at the Las Vegas market that didn't add any new resorts, revenue was only up 1.1%, which isn't impressive by any measure. 

To make matters worse, there's been concern in the market that trade conflicts with Mexico and China could slow the U.S. economy and eventually lead to a recession. 

Now what 

Gaming stocks can swing wildly based on even the threat of a slowdown in the market and that's what we're seeing for Boyd Gaming right now. Whether it was Penn National's disappointing results or the market's reaction to increasing trade tensions, shares were under pressure all month. I don't think there's a reason to fundamentally change your thesis on Boyd Gaming as a stock, but understand that this is part of the volatility of owning gaming stocks long term.