Alphabet's 2.3% slide cost Communication Services more than Charter's 8% crash

Alphabet lost about $94.3 billion in market value on September 9 - more than Charter Communications and Comcast lost combined, even though Charter and Comcast were the two stocks that made headlines for crashing that day.

Communication Services was the worst-performing sector in the S&P 500 on September 9, down 2.26% on a market-cap-weighted basis while the index itself slipped only 0.45%. (Energy was the best performer, up 1.09%.) Across the sector's 16 members, that 2.26% translates to a combined $118.4 billion drop in market value, based on the day's market-cap snapshot.

Most of the day's headlines went to the cable and broadband names. $CHTR fell 8.13%. $CMCSA fell 6.61%. $TMUS fell 2.39%. Those moves followed comments from Comcast's own CFO at the Goldman Sachs Communacopia + Technology Conference, where he described broadband and fiber-internet pricing as "irrational" - a remark Bloomberg linked directly to the stock's slide. Yahoo Finance and 24/7 Wall St. both framed the session as a possible "broadband repricing," noting that Comcast, Charter and T-Mobile were all falling together.

T-Mobile's own move got less attention than Comcast's or Charter's, but at 2.39% it was actually close to the size of Alphabet's decline in percentage terms - a reminder that the "broadband repricing" framing swept in a wireless carrier alongside the cable operators.

Percentage moves and dollar moves are not the same thing, though, and the sector's three most-quoted decliners are also three of its smaller companies by market cap.

$CHTR's entire market cap is $18 billion, so even an 8% drop only erased $1.6 billion. $CMCSA, worth $87.3 billion, lost $6.2 billion on its 6.61% decline. Add $TMUS's $4.7 billion and the three most-discussed decliners of the day lost about $12.5 billion between them - a little over a tenth of the sector's total loss.

$GOOGL moved a comparatively quiet 2.28%. But at a $4.04 trillion market cap, that was enough on its own to erase $94.3 billion - about 80% of the entire sector's loss, more than the other 15 members of Communication Services combined, and roughly seven and a half times what Charter, Comcast and T-Mobile lost together.

Alphabet's decline landed the same day Google rolled out search changes across the EU to comply with regional antitrust rules, warning that the changes would make results worse for users, according to TradingView's report on the rollout. That is a separate story from the broadband-pricing comments driving the cable stocks - different company, different regulator, different business. Both stories broke on September 9, both companies sit in the same GICS sector, and only one of them moved anywhere near $94 billion.

That is the gap between what shows up in a headline count and what shows up in a treemap. A story about three companies "sinking" and "dropping" and "slipping" reads like the day's dominant theme, and by number of stocks falling hardest, it was. But Communication Services is a $5.1 trillion sector with one company that is nearly 80% of it. When that company moves even a little, it outweighs almost everything else combined - no matter which stock's percentage decline is doing the talking in the headlines that day.

Out of the S&P 500's 500 constituents, only 16 sit in Communication Services, and only one of them is large enough to move the sector on its own. That is worth remembering the next time a sector-level number gets attributed to whichever stock had the loudest headline.