Between FY2019 and FY2024, 93 per cent of individual equity Futures and Options (F&O) traders on the National Stock Exchange (NSE) incurred net losses, prompting the Securities and Exchange Board of India (SEBI) to introduce a sequence of escalating regulatory interventions. This study identifies which of nine SEBI interventions — spanning a weekly expiry introduction (2016), stock eligibility tightening (2019), phased peak-margin requirements (2020–2021), weekly expiry restriction (2023), and a combined lot-size and income/knowledge eligibility package (2024) — produced statistically significant causal changes in retail F&O participation in India from January 2015 to January 2026.

Using a multi-intervention Interrupted Time Series (ITS) framework across 133 monthly observations, the study estimates each intervention's effect on three outcomes: active unique retail traders (Y1), retail turnover share (Y2), and new F&O registrations (Y3). All models control for the COVID-19 participation shock (a mandatory step dummy isolating a +14.22 lakh surge, March 2020–March 2021), the secular time trend, market volatility (India VIX), Nifty 50 returns, discount broker penetration, retail search attention, and mobile internet growth.

Structural interventions produced substantially larger participation reductions than incremental capital-cost measures. The October 2024 lot-size increase (D5a: −12.47 lakh***), income/knowledge eligibility criteria (D5b: −10.22 lakh***), and October 2023 weekly-expiry restriction (D4: −8.64 lakh***) each far exceeded the phased peak-margin effects (D3a–D3d: −1.47 to −2.85 lakh per phase). The liberalising weekly-expiry introduction (D1: +2.41 lakh**) confirms bidirectional sensitivity. Market conditions moderate deterrence: bull-market returns attenuated the D3 effects; weak FY25 returns amplified D4 and D5. Discount broker penetration offsets approximately 30 per cent of the D5b entry barrier. Retail turnover share (Y2) is formally excluded from D5a specifications due to lot-size-induced denominator endogeneity. All findings are robust to a post-2017 restricted sample.

The study contributes a validated multi-intervention ITS design simultaneously addressing COVID-era confounding, market-condition moderation, technology-access offsets, and a

novel endogeneity correction for the lot-size change — the first such unified framework applied to the Indian equity derivatives market.