New Delhi, July 5 -- The Indian stock market regulator's action against Jane Street after the alleged index manipulation came to light has reignited concerns over just how exposed and powerless retail traders remain in the high-stakes world of derivatives trading.

The Securities and Exchange Board of India (SEBI) on July 3 temporarily barred Jane Street from accessing the Indian stock market and also impounded Rs.4,840 crore from the US trading firm, which the regulator claimed is the total amount of "unlawful gains" made by it.

In its 105-page order SEBI, in detail, flagged the "manipulative" and "fraudulent" trades by Jane Street that mostly took place in the Nifty Bank Index's weekly options contracts and its underlying constituents ...