OK, I didn't make it up. There is plenty of historical evidence about the way the Celts fought against the Romans for instance - which is where the idea came from. The Osprey book on the Celts "Lords of Battle" p122 - p128 gives a good summary and includes quotes from Caesar, Tacitus etc. ...

I have been thinking about the "Barbarians vs Legionaries" debate and I have an idea. Why not have a -1 on cohesion tests for undrilled troops losing an impact round vs drilled and visa versa? This would simulate the disadvantage of drilled troops losing cohesion vs a successful barbarian ...