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This is the most important level to watch on the S&P, says equity strategist

Why the S&P's 200-day moving average could be a make-or-break level for stocks

After an unusually volatile string of sessions for U.S. equity markets, stocks have kicked off the week relatively calmly. Amid the market swings, one chart-minded strategist has identified a key level for the S&P 500 which carries significance for other major markets, too.

The 200-day moving average has proven critical support for the , according to Matt Maley, equity strategist at Miller Tabak. He is now eyeing the 200-day moving average as key support for other indexes, as well. Here are his reasons.

• The 200-day moving average on the S&P 500, which on Tuesday came in at 2,541, has proven solid support for the S&P 500. The S&P dipped just below that level on Friday before closing the day higher, but before that it hadn't been tested since November 2016.

• Not only is the 200-day moving average significant for the S&P, but it has proven good support in the Russell 2000, the popular iShares emerging markets exchange-traded fund (EEM) and the Japanese Nikkei.

• Investors are going to be watching the individual 200-day moving averages across these key markets and ETFs around the world. The moving average is a common indicator that takes the average closing price over a particular period of time, in this case 200 days.

• If any of these markets experience significant pullbacks that violate their respective 200-day moving averages to the downside, this will be quite significant on a technical basis for the rest of the first quarter.

Bottom line: The 200-day moving average is a significant level for not only the S&P 500 but for the Russell 2000 and one popular emerging markets ETF as well, according to one strategist.