I was born and raised on a horse / cattle ranch and worked with quite a few draught horses, used to ride them for fun, really hard to ride, legs and hips don't want to spread that wide! But boy oh by are they powerful!
I had two favorite horses Red a Belgian, and Pride a thoroughbred.
Pride was an excellent cattle horse, normally you use a quarter horse (they are shorter and stockier), Pride's advantage was he was fast, he could get in front of a heard and turn them.
Rode hundreds of miles of fences and fields on him, remember a few nasty snow storm where I had no idea where camp or home was and I'd just throw the reins over his neck and let him do the driving!
To all that are confused about, the docking.
There is two different meanings going on here:
Yes they were going to do a doing a docking procedure with the Team.
Exceptionally hard with an eight horse hitch.
#1:
The horses work together with the teamster, backing and maneuvering the hitch Wagon to the foot of the loading dock.
One of the hardest things to do with any horse is to get them to back up, it's just not a natural movement for them.
#2:
Surgically removing their tails (at a very young age).
This is done so that they don't get their tails caught in the rigging and harness.
While it is viewed by some as cruel, it's done to keep them from getting hurt doing their job.
Same reason you poll (cut off) the horns on cattle to keep them from hurting themselves and others.
I will say watching the video, I think I know why the lead team did what it did.
It wasn't a dominance thing, it wasn't any horse error, it was the drivers error.
As they stopped the driver took up the reins (steering and speed control for the city folk among us), the front wheel team ( third from the front) was spread wide, they moved in and he took up more, then one moved out and thus the right rein was too tight, the lead team (front) started to steer right, both the driver and the shotgun rider looked to the rear, and when he did that he pulled the right rein and with the front team turning into a fence, turned fast and hard which pulled the rein even tighter which put them into an uncontrolled turn.
Horses are trained to do what the reins and driver tell them to do.
Its excellent that this turned out as well as it did for all, as a tangled up team can panic and all heck breaks loose!
P.S. Horses don't typically lay down, they sleep standing up! The bigger the horse the less libel they are to lay down. So when they fall down, or in this case get knocked down, they have a real hard time getting up!