Several high‑beta stocks saw outsized moves in MarketWatch’s list of S&P 500 laggards at the end of the week.

In MarketWatch data last updated March 20, 2026 (5:05 p.m. EDT), Super Micro Computer (SMCI) was shown down 33.32% on the day, leading the “Bottom Performers” table on the S&P 500 index page.

Other decliners highlighted in the same MarketWatch snapshot included:

• Vistra (VST): -12.64%

• Constellation Energy (CEG): -10.90%

• Mosaic (MOS): -9.96%

• NRG Energy (NRG): -9.67%

On the upside, MarketWatch listed several “Top Performers,” including:

• Marsh (MRSH): +3.26%

• APA Corp. (APA): +2.76%

• Aon (AON): +2.73%

Big single‑stock moves can reflect company‑specific headlines, positioning, or broader risk‑on/risk‑off swings. Regardless of the trigger, sharp percentage moves often feed into wider index volatility, a dynamic reflected in the same MarketWatch dashboard by an 11% jump in the VIX.

Investors typically watch whether these outliers see follow‑through in the next session, especially when broader indexes are trending lower.