Overview
In a film crew, there are two kinds of best boy: best boy electric and best boy grip. They are assistants to their department heads, the gaffer (in charge of electricals) and the key grip (lighting and rigging), respectively. In short, the best boy acts as the foreman for the department. A woman who performs these duties may be called best girl. Recently, some film crews are adopting gender-neutral terms for job titles, and one example of this is the use of 'lead electric' as a replacement for the term 'best boy' in the electrical department.
Job responsibilities
Best boys are responsible for the day-to-day operation of the lighting or grip department. Their many responsibilities include the hiring, scheduling, and management of crew; the renting, ordering, inventory, and returning of equipment; workplace safety and maintaining discipline within their department; completing timecards and other paperwork; stocking of expendables; loading and unloading production trucks; planning and implementing the lighting or rigging of locations and/or sound stages; coordinating with rigging crews and additional photography units (if applicable); handling relations with the other production departments; overseeing the application of union rules (where relevant); and serving as the day-to-day representative of the department with the unit production manager and coordinator of their department.
The best boy also commonly accompanies or stands in for the key grip or gaffer during technical scouts. During shooting, the best boy may also cover for the key grip or gaffer when he or she is on a break or otherwise away from the set.
On films with very small crews, the electricals (lighting) department often consists of only a gaffer, a best boy, and a few electricians. The grip department may include only a key grip, a best boy, and a few grips. Large-scale productions such as major films commonly include full-time rigging and second unit crews, and in total may hire many dozens of grips or electricians at one time.
From Wikipedia (CC BY-SA 4.0).