Positioning and awareness of where archers are, basic stuff..
If you get a shield, you might be able to avoid getting shot for some time then, if you don't try to actually go towards the archers. If you go towards the archers, you will most likely be shot in your sides or even your back, because they will start splitting up. Ontop of this, archers are usually way in the back, so you will most likely also be fighting melee, which is a possibility for a 1h/shielder, but not really for a 2h/polearm with a shield, since they can't both fight and stay protected from archers at the same time, not properly.
If we however imagine that there is no melee around them, then you still have the problem with the split archers, which means that if you have chase one, then the other one will shot you in the back. This of course goes on, while the archer you're chasing is running away. This is why just ''get a shield'' is far from enough. A shield might be able to delay your death, but it won't really change the result by much.