Who is on the other side

An ES order book is a few thousand contracts resting on about twenty levels on each side, and a flow of executions of several thousand contracts per minute during the session. Behind it, five families of players, and only one of them has no opinion. Knowing who does what in the book changes the reading of every wall and every burst.

The only player without an opinion

The options market maker makes a living on the spread between buying and selling, not on direction. When a client buys a call from them, they are short the call, hence short delta: they buy ES to get back to zero, and they become short gamma. When a client sells them a put, they are long the put: they also buy ES, but they become long gamma. The sign of gamma does not depend on the type of option, only on who is the buyer. Module 4 details the mechanics; for now, remember that these readjustments are real orders, without opinion, and that they can be mapped.