But if we're talking only whats displayed in the film, I believe that RM rules could be used to justify some of the maneuvers.
I don't have much time, heading to work, but here's a quick rundown.
1. Cover: Interlocking shields could actually provide Full hard cover for those inside and pretty good Partial cover for those on the outer edge of the turtle formation.
Or, there is a pretty good rule in a RoCo about adding the DB of shields if 2-3 guys have them in a line, against that facing.
2. Massive combat skills: The portrayal in the movie shows warriors that excel in combat. They always seem to know where an enemy is within their combat reach. Sit-Aware Combat, Two-handed Combat, Shield Bash, Reverse stroke (to add OB/DB to rear attacks).
You could also use Reverse stroke to add OB to rear attacks.
Pretty good Tactics as well. The entire group gets an OB bonus.
Awesome Adrenals from SD and even Power Attacks, for some.
Then there Stun relief and skills to lower crits from attacks..
These may be obvious to everyone but just some thoughts.