Why It Moved · Market · 2026-10-28
Why it moved, October 28: Fortinet -27%, F5 -20%, ServiceNow -19%
On Wednesday, October 28 the S&P 500 rose 0.3% and 251 of 503 member stocks finished higher. These were the five biggest moves among S&P 500 stocks, and what was behind each.
Investigations
The question
Revenue grew 11% from a year earlier and the company made money, yet the stock fell 21% around its results. What do the filings show that the headline didn't?
What the filings show
- Insiders sold, none bought. Executives and directors sold about $5.2 million of stock in the 90 days to Oct 28, the largest seller $1.8 million. Sales are often planned or for taxes; purchases are rarer.
- The timing. Results came out after the close on Oct 27. The stock moved -0.5% that day, before they were public (S&P 500 ETF +0.6%), and -20.4% the next day (S&P 500 ETF +0.1%).
- Outlook cut. The company's own revenue outlook for the full year moved to $8-$9, from $9-$10 in its previous release.
What to watch
- The next quarterly report (the quarter ending in September, filing due around November 2026): whether the outlook holds.
Sources: earnings release (8-K, 2026-10-27) · 10-Q (2026-08-06)
The question
The share count is growing fast. Who is paying for the growth?
What the filings show
- More shares. The latest 10-Q/10-K cover page counts 1,034.0 million shares, up 397% from 208.0 million a year earlier - each share owns a smaller slice of the company.
- Outlook raised. The company's own revenue outlook for the full year moved to $3.2 billion-$3.3 billion, from $406 million-$410 million in its previous release.
What to watch
- The next quarterly report (the quarter ending in September, filing due around November 2026): the share count on the cover page.
Sources: earnings release (8-K, 2026-07-22) · 10-Q (2026-07-23)
The question
Revenue grew 18% from a year earlier and the company made money, yet the stock fell 18% around its results. What do the filings show that the headline didn't?
What the filings show
- Insiders bought. Open-market purchases of $2.5 million in the last 90 days, against $253,110 of sales.
- The timing. Results came out after the close on Oct 27. The stock moved -5.0% that day, before they were public (S&P 500 ETF +0.6%), and -13.9% the next day (S&P 500 ETF +0.1%).
What to watch
- The next quarterly report (the quarter ending in September, filing due around November 2026): whether the outlook holds.
Sources: earnings release (8-K, 2026-10-27) · 10-Q (2026-07-29)
The biggest S&P 500 moves, October 28
"vs usual day" compares the move with the stock's average daily move (up or down) over the past year. "Where it stands" is the distance from the 52-week high and the position against the 200-day average. Stocks with a one-day change over 60% today (usually a spin-off or split) are left out; where a stock had such a jump earlier in the year, its longer-run columns show –.
What this means
- Fortinet (FTNT) fell 27.0% as Benzinga reported “Fortinet Stock Tanks After Q3 Earnings Print: Details”1. That is about 14 times its usual daily move. It was not alone: the other 6 software stocks in the S&P 500 fell a median 3.3%, 4 of the 6 lower (biggest: ServiceNow -19.2%, Palo Alto Networks -6.7%, CrowdStrike -6.3%). It reported quarterly results; options had priced a move of about ±29%.
- F5 (FFIV) fell 20.4%. That is about 12 times its usual daily move. Its networking peers barely moved (median -0.1%), so this was about the company, not its industry. It reported quarterly results.
- ServiceNow (NOW) fell 19.2% as Bloomberg reported “ServiceNow Falls After Quarterly Sales Outlook Revives AI Fears”2. That is about 7 times its usual daily move. It moved with the rest of the software group (see Fortinet above). It reported quarterly results; options had priced a move of about ±21%.
- CoStar Group (CSGP) fell 13.9%. That is about 7 times its usual daily move. It reported quarterly results.
- Vertiv (VRT) rose 13.4% after the company raised its outlook3 and a new partnership4. That is about 4 times its usual daily move.
- A big one-day move tells you what the market learned that day, not where the stock goes next: large moves partly reverse about as often as they continue.
Sources
- Benzinga, Oct 28, 2026: Fortinet Stock Tanks After Q3 Earnings Print: Details
- Bloomberg, Oct 28, 2026: ServiceNow Falls After Quarterly Sales Outlook Revives AI Fears
- Investopedia, Oct 28, 2026: Nvidia Partner Vertiv Leads S&P 500 Gainers After Strong Earnings, Raised Outlook
- Investor's Business Daily, Oct 28, 2026: Nvidia Partner Vertiv Soars After Blowout Earnings, Strong Guidance
Did the model see it coming?Subscribers see the model's view on every S&P 500 stock before and after big moves.
See plans
Prices from Torvanta's end-of-day data; filings from SEC EDGAR. News context is drawn from the coverage cited below and may not be the whole cause of a move. Research only, not investment advice or a recommendation to buy or sell any security. Rankings change as data changes and can be wrong. Torvanta and its founder may hold positions in securities discussed, and trade only after the information is published to all subscribers. Past performance does not guarantee future results.
More research
- Market brief, Thursday October 29: futures little changed 2026-10-29
- Fair Value Check: Berkshire Hathaway is overvalued on our numbers 2026-10-29
- The Giants Monitor: the top 10 are 42.0% of the S&P 500 (week of October 26) 2026-10-29
- Insider & Short-Selling Daily, October 28 2026-10-28
- Market brief, October 28: S&P 500 rises 0.1% as software stocks slide 2026-10-28
- Midweek Movers: where the model's view shifted this week 2026-10-28
- Insider & Short-Selling Daily, October 27 2026-10-27
- Market brief, October 27: S&P 500 rises 0.6% as chip stocks rally 2026-10-27
- Why it moved, October 27: Xylem -14%, Pentair +13%, Boeing -11% 2026-10-27
- Dividend Watch, October 27: Vici Properties leads covered yields 2026-10-27
- Insider & Short-Selling Daily, October 26 2026-10-26
- Market brief, October 26: S&P 500 rises 0.7% as chip stocks rally 2026-10-26
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