The party in a trade that initiates the deal. The aggressor works with the dealer, who takes a passive role and posts the bid and ask quotes. The aggressor in a transaction will typically attempt to instigate the deal and push it forward in order to obtain financial benefit.

In order flow, trades are considered "positive" or "negative" depending on whether the aggressor is buying or selling. For example, an aggressor selling 10,000 units will create an order flow of -10,000 with the dealer. Because commodity futures must have a buyer and seller who execute a trade simultaneously, the dealer in the aforementioned example will have a positive 10,000 order flow.