What typically goes to second unit
Anything that doesn't need the director standing next to the camera or the lead actors' faces. On a fictional thriller that could be:
- EXT. HIGHWAY - DAY: driving plates for three car interiors (process work later on stage)
- EXT. CITY SKYLINE - NIGHT: establishing shots for four scenes
- Sc. 88: the car flip, with stunt doubles for Maya and Joe
- Inserts of hands on a steering wheel, a phone screen, a key in a lock
Each item gets strips on a second unit board, and second unit gets its own call sheet with a separate crew list. A second unit day is listed as "2nd Unit Day 3" so it doesn't get confused with main unit's day count.
How it fits with main unit
A second unit may shoot the same days as main unit in another place, or on days after main unit wraps. The 1st AD of main unit and the second unit AD coordinate constantly, especially over shared elements: picture vehicles, stunt performers, wardrobe doubles, and props. If main unit needs Joe's car at 2:00P, second unit can't have it for plates that afternoon.
The DGA Basic Agreement requires the producer to consult the director on the second unit director and to disclose, before principal photography, what material is intended for second unit (DGA Basic Agreement Article 7).
Stunt days and doubles
Stunts are a large share of second unit work on action shows. The stunt coordinator may double as second unit director. The pages count for a stunt can be tiny (sc. 88 is 2/8 page) while the unit needs a full day with safety meetings, rigging, and rehearsals. Faces for the stunt usually come from main unit later, shot in close-up with the actors on a controlled rig, so both boards need to agree on what's being shot where.
Where it goes wrong
Continuity drift is the big one. Second unit shoots the car in daylight on a sunny day in week 6, and main unit shot the matching scene under cloud in week 2. Second unit needs the script supervisor's notes, stills, and a clear brief on lens, time of day, and weather.
Budgets also underestimate it. A second unit carries its own camera package, grip and electric, transport, and often permits. On smaller shows a splinter unit or pickup shots inside main unit days can cover the list for far less.