Dealer gamma (GEX): why the market pins on some days and chases on others
When you buy an option, a market maker sold it and hedged it with the underlying. Those hedges are mechanical, and in aggregate they move the market.
Positive gamma pins
When dealers are net long gamma (customers sold them calls), they sell into rallies and buy dips to stay delta-neutral. That hedging leans against every move; the index pins near the strikes with the most gamma. Sellers love these days.
Negative gamma chases
When dealers are net short gamma (customers bought protection), they must buy as the market rises and sell as it falls. Their hedging pushes the move further. Breakouts run, gaps extend, and short premium bleeds.
The flip level
Summing dealer gamma across strikes gives a curve that crosses zero at some price: the gamma flip. Above it the market is in pinning mode, below it in chasing mode. Knowing which side of the flip you are on is worth more than most indicators.
Where to see it
The terminal's GEX panel computes dealer gamma by strike from open interest in rupee crores per 1% move for NIFTY and BANKNIFTY, marks the flip, and the alert engine can wake you when the flip moves. Read it with the OI build-up tags from OISCAN and the structure drawn by the VIP Indicator and the day's behaviour stops being mysterious.