Mumbai, Oct. 5 -- Trading activity in Indian stock markets fell sharply in the September quarter, with volumes in both the cash and derivatives segments declining as rising global bond yields, foreign outflows and new regulatory curbs on traders weighed on sentiment. The combined average daily equity cash volume of NSE and BSE fell 11.7% sequentially to Rs.1.29 lakh crore in July-September, reversing a 13% rise in the preceding quarter, according to exchange data. The combined average daily index-options premium volume fell by a sharper 27% to Rs.63,326 crore over the same period-extending an 11% decline in the April-June quarter, and marking a second straight quarterly drop. The slowdown reflects a confluence of pressures. A surge in oil prices, driven by the US-Iran war and disruptions to global supplies, has pushed up bond yields and heightened volatility, while US Treasury yields-at their highest level in more than two decades-have driven foreign investors out of Indian assets. A revival in volumes may hinge on two swing factors: a de-escalation of the war in West Asia, and whether the market regulator delays rules pertaining to weekly options settlement on expiry days. "Incremental flows have clearly reduced as investors have been losing by averaging on the downside, which is behind fewer transactions in both cash and derivatives segments," said independent market analyst Ambareesh Baliga. Baliga also said that the Reserve Bank of India's (RBI's) funding curbs on proprietary traders, and teething troubles with the Securities and Exchange Board of India's (Sebi's) newly introduced closing auction, have dented domestic participation in both cash and derivatives markets. The Nifty 500 declined 4% to 22,072 during the September quarter-a sharp reversal from the nearly 10% gain it posted in the first quarter of FY27. The reversal mirrors oil's own swing - Brent crude rose 34% to $98 a barrel during the September quarter, after sliding 38% to $73 a barrel in the June quarter, according to Investing.com. The sharp rise in crude prices has been a primary reason for the market's underperformance. Foreign portfolio investors sold Rs.1.38 lakh crore of Indian equities in the fiscal year through October 1, after a record Rs.1.8 lakh crore of selling in FY26, adding to market volatility and weighing on overall participation. Following this, the yield on the benchmark 10-year Indian government bond rose 43 basis points (one basis point is one-hundredth of a percentage point) to 7.18% during the September quarter, according to Investing.com. Hopes of a resolution to the West Asia conflict had driven the yield down by 21 basis points to 6.75% during the first quarter. Other factors weighing on volumes include an RBI regulation requiring banks to fund proprietary traders only against full collateral from July, and the new closing auction session (CAS) introduced by Sebi from 3 August. "Q2 has been a bit challenging for the broking industry," said Ashish Nanda, chief digital business officer at Kotak Neo, underscoring the fall in volumes. Analysts are split on the prospects for a recovery in volumes, especially in the cash market, but expect options volumes to pick up if Sebi defers the CAS requirement for derivatives settlements on weekly expiry days....