Options traders on Friday concentrated activity in the S&P 500’s 6400 strike, turning that level into the most actively traded call on the board. Market participants cited a build-up of same-day-expiry contracts and a resulting “call wall” that has drawn the cash index toward the level in late-session trading. Analysts tracking gamma exposure said the cluster of positive gamma around 6395–6400 is acting as a magnet, while the absence of significant positive gamma until roughly 6410 could open a further move if 6400 is breached. The dynamic has encouraged dip-buyers throughout the afternoon as they attempt to push the benchmark through what several desks described as a key resistance zone.