Blame that on a selloff in tech high-fliers popular among amateur investors and a widening rotation into value names. Declines in stocks from Tesla Inc. to Plug Power Inc. slowed retail traders' appetite for upside calls and triggered a spike in demand for downside loss protection, data compiled by Barclays show.

The individual-stock skew, or cost of hedging against single-stock losses relative to gains, spiked as a similar measure for the broader index declined (as gains in one part of the stock market offset losses in the other.) As a result, a months-long gap between retail euphoria and institutional skepticism all but disappeared.

"The equity selloff had a larger impact on retail investors as large-cap tech/growth stocks which generally overlap with retail favorites took a bigger hit, relative to other sectors," Barclays strategists including Maneesh Deshpande said in a note to clients.