Why BellRing Brands Dived by Nearly 10% Today

It will soon no longer be a component of the S&P 400 MidCap index.

Investors should be aware that this will have little to no effect on its fundamentals.

Many investors weren't eager to ring the bell for BellRing Brands (NYSE: BRBR) during Monday's trading session. Shares of the protein products maker slumped by nearly 10%, on news that its stock is being dropped from a high-profile index.

After market close on Friday, S&P Global announced the latest quarterly rebalancing of its closely followed S&P family of indexes . One of those lineups that will see adjustments is the one BellRing is currently a part of, the S&P MidCap 400 index. The company's stock is one of five being moved and replaced with new arrivals; the four others are Flex , Coty , Concentrix , and Blackbaud . Those four are being shifted to different indexes more appropriate for their current size.

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The quintet of incoming S&P MidCap 400 stocks comprises Roku , Coeur Mining , Semtech , Sanmina , and Viavi Solutions .

These changes, which, in S&P Global's boilerplate language, are being made to "ensure that each index is more representative of its market capitalization range," will take effect before market open on Monday, June 22.

I should stress here that inclusion in, or exclusion from, a famous stock index almost always has little or no impact on a company's fundamental performance. In BellRing's case, however, a skinnier market cap is indicative of its recent struggles , and the reminder is a likely reason for Monday's sell-off.