This is what FII's & other large players do. Their buying and selling impact prices immensely. They buy options on expiry day and then buy or sell to minimize the impact cost.
We were out after booking profits in the range of 19150-275 and were waiting on the sidelines once it crossed 19300 with force, jumped in again and captured the next 200 points in last one hour. All profits booked.
Now, will wait for BankNifty to touch 19200-300 and will buy again.