Some traders doubled their money with big bearish bets on Snap just before the plunge

• Snap reported weaker-than-expected results, sending the stock down 20 percent and crushing investors. But some traders made a bold bet before the release that Snap's results would whiff.
• Jon Najarian, co-founder of the Najarian Family Office, said the May $24.50 puts spiked from $2.75 to $6.50 and the August $21 puts jumped from $2.10 to 4.29.

A person holds up a pair of Snapchat Spectacles by Snap Inc. on the floor of the New York Stock Exchange (NYSE) during the company's initial public offering (IPO) in New York, March 2, 2017.

Michael Nagle | Bloomberg | Getty Images

Most investors got crushed in Snap on Thursday after the company's first-quarter miss, but some traders made a killing on the social media firm's stock plunge with big bearish bets just before the close Wednesday.

Snap reported sales of $150 million versus a Wall Street consensus of $158 million Wednesday after the close. The social media firm also posted a wider-than-expected loss.

The stock then plummeted as much as 23 percent in trading Thursday.

Jon Najarian, co-founder of the Najarian Family Office, told CNBC in an email that some traders bought a "large" number of put contracts near the close of regular trading and just before Snap released its first-quarter results.

Traders who made these bearish bets essentially doubled their money. Najarian said the May $24.50 puts spiked from $2.75 at time of purchase to $6.50 Thursday and the August $21 puts jumped from $2.10 to $4.29 Thursday. Snap's stock was below $19 Thursday, putting these options deep in the money.

Snap 2-day chart

Source: FactSet

Puts are options that give the owner the right to sell a stock at a given price within a specific period of time.

"Now, there are two basic reasons that someone buys a put contract; 1) to protect their long position in the equity 2) to bet that the equity may decline. When they scramble into puts in the final 5 minutes of trading, we think that's pretty telling," Najarian said.

"Under normal circumstances, I would have tagged these trades and followed into puts of SNAP and subsequently, reaped a big windfall. Sadly, last night the paper came so late in the session that we didn't participate," the trader added.

Disclosures: Jon Najarian is a frequent guest on CNBC's "Fast Money: Halftime Report." CNBC parent NBCUniversal is an investor in Snap.