The 15 worst-performing S&P 500 stocks during a dismal September

September is living up to its reputation as the weakest month of the year for U.S. equities. While the S&P 500 has managed a slight gain, that headline number masks a lopsided market: roughly three-quarters of the index's components have declined, with leadership concentrated in a small group of large-cap names. The result is a familiar divergence — a resilient index level paired with widespread weakness beneath the surface.

The 15 worst performers span a range of sectors, suggesting the pullback reflects broad risk reduction rather than a single industry-specific shock. For market observers, the key takeaway is that index performance alone can overstate overall market health. When a handful of heavyweights drive gains, breadth measures — such as the advance-decline line or the share of stocks above key moving averages — can deteriorate even as the index rises.

What to watch from here: whether September's softness persists into October, a month historically associated with elevated volatility, and whether breadth improves or narrows further. Neither outcome is predetermined, and past seasonal patterns are not guarantees of future results.