The head of New York hedge fund Melvin Capital Management is making a $400 million short bet against Nintendo, according to Bloomberg.

Gabriel Plotkin’s fund was short 1.2 million shares, or about 0.8% of Nintendo’s outstanding stock, according to the latest filing with the Tokyo Stock Exchange. Bloomberg said it’s the largest such trade against the company since at least 2013.

“Investors have been baffled by the sudden swoon and Plotkin’s position may add to their concerns,” Bloomberg’s Yuji Nakamura said. “The stock’s poor performance has dominated coverage in the financial and gaming press, and discussions on social media, raising questions about whether long-term shareholders are losing faith in the outlook for the Switch game console.”

Nintendo had an impressive 2017 financially thanks to the launch of the Switch. It sold an estimated 17.79 million units, beating its own prediction of 15 million. The company believes it can sell 20 million more this financial year. Operating profit reportedly rose by 505% to 178 billion yen and revenue was up 116% to 1.06 trillion yen.

But, the company inexplicably suffered its biggest two-day drop since December 2016 in June during E3, Bloomberg reported. Some analysts blamed it on a poor Switch lineup. Nintendo refuted those claims. Shares have now fallen as much as 27% from their peak in May. Bloomberg said Plotkin increased his short position on both days after E3 and continued short-selling in the following weeks.

Nintendo shares closed at 37,540 yen Monday, down 8.9% for the year. The company will release its first quarter earnings report on Tuesday after the market closes.