SanDisk Corp. (SanDisk (SNDK)) is having a rough Monday. The stock fell 12%, making it the worst performer in the Russell 1000, and extending its decline to more than 45% from the record high it hit back in June. Ouch.

This isn't a one-day freakout. Friday's session saw a 10.8% drop, and the selling has been building as investors get more nervous about Chinese memory makers muscling into the NAND flash market. The latest spark? ChangXin Memory Technologies' blockbuster IPO in Shanghai. That deal renewed fears that Beijing's push into memory chips could lead to oversupply and crush industry pricing.

Technically, things just got uglier. Monday's slide pushed SanDisk below its 100-day moving average for the first time since August 2025. That's a level traders watch closely, and breaking it is usually seen as a bearish signal.

So what's the story? Investors are pricing in the risk that Chinese competition will eat into SanDisk's profits, and the market is voting with its sell orders. For now, the trend is not SanDisk's friend.