Street gangs exhibit varying degrees of structure, organization, and cohesion. They aren't all tightly knit or highly structured by any means. Some are very cohesive criminal enterprises with clear and strong leadership at the top, while most are loose confederations of youth and adults whose associations grow out of the shared troubles of their respective biographies. Street gangs are hard to define for other reasons, too. As porous social groups, gangs experience tremendous turnover of members.
Youth come and go, often staying involved for about a year before moving on.
Gang leadership also changes over time. A leader today may be gone tomorrow because of a family move, voluntary disaffiliation, or incarceration. Another challenge to defining the street gang is the ambiguity surrounding gang membership. That the group itself defies precise definition makes it equally difficult to define and identify the gang member. The constant flux of the typical gang's membership and leadership make the street gang hard to define.