Things I have learned regarding a riot shield line:
They fight a lot like Roman Legionaires. You will not break them by charging. You will not break them by shooting, unless you go big dakka.
One good way to break a line of tustedo would be to use Elephants. The modern and superior equivalent would be a Forklift truck.
A single Viking in a forklift truck could decimate the entire line and break the police kettle, leaving plenty of space for more Vikings to rush through. The fight would be over soon as the wall faltered and the cumbersome shields met axe and spear.
So the question is, did the Vikings historically use Forklifts in battle?
As the battle of Stamford Bridge shows, yes. It is why Harold Godwinson attacked the Vikings first instead of the Normans. He feared that would the Vikings successfully employ their Forklift trucks, all would be lost. So he rushed North to make sure they would not survive preparations. Attacking before the Vikings could employ their Forklift trucks was a brilliant strategical move, and knowing confusion defeat, Harold Hardrada ordered the Vikings to destroy the few surviving trucks; a devastating blow to Harold Godwinson who wished to use them against the Normans. Viking Forklift trucks would never be seen again as heavy infantry fell from the spotlight of conventional warfare.
Vikings: 1
Riot police: 0
Saxons: Sour
Normans: Stole their kill LOL