best boy 
noun
The assistant to the chief electrician of a film crew.They brought the best out of everyone on their staff, from the actors to the cinematographers to even the best boy (who makes a small cameo in one of the bar scenes)....
- The boom guy doesn't criticize the best boy; the assistant director doesn't call in sick.
- Some DV films are made with no soundman, no lighting expert and none of the other odd-jobbers (key grip, best boy, assistant gaffer) who show up in the closing credits of big productions.