Illegal wild capture fisheries undermine crustacean (e.g., crabs, lobsters, and swimming crabs) stock and their habitats. In a search for a new approach to the fisheries issues, this paper aims to explain why the illegal fishing for crustacean species still exists in Indonesia. It focuses on analyzing a set of practices in crustacean production and consumption. Banyuwangi (Indonesia) was the case study area of the conducted fieldwork. The method applied semi-structured interviews and participant observation. The design of research enabled the researcher to study daily fishing, purchasing, and processing. These practices determined the exploitation of crustacean species in the sea. This paper shows that the current fishing, purchasing, and processing of crabs, swimming crabs, and lobsters played a vital role in constructing the habit of illegal fishing. When the catch prohibition rules heavily focused on the wild capture fisheries in the sea, the local intermediaries and processors innovated their purchasing and processing to obtain crustacean species incessantly. Such an innovation was in response to the crustacean scarcity problems. (1) In swimming crab mini-plants, processors diversified their processed swimming crab products. The crab product diversification allowed them to process swimming crabs in all sizes. (2) The local intermediaries gave fishermen binding loans. Fishermen paid back the loans by supplying the crustacean species to the loan givers. (3) The existence of processing and purchasing stimulated fishermen to harvest every last crustacean species. Even though such crustacean fishing was illegal, it contributed to the livelihoods of fishermen, local intermediaries, and processors. This paper makes a research contribution to the use of social practice theory in fisheries issues. It gives a novel research approach to the habit of illegal fishing problems.