A Man-At-Arms Rush is a common Strategy and is often followed by Archers, Towers or Scouts. The advantage of going into Man-At-Arms over Scouts is that you can make 3 Militias in the Dark Age while aging up to the Feudal Age, meaning you'll have 3 Men-At-Arms at the opponents base before they have even produced a single Scout. Signs that indicate a Man-At-Arms opening are A, 2 villagers on gold. B, 4 villagers on wood. And C, a Barrack around 8 minutes starting to queue Militias. With this in mind, the best counter would preferably be to fully wall into Archers. If your economy is already set for Scouts, wall to the best of your abilities and don't engage his Men-At-Arms before you have atleast 4 scouts, micro away the Scouts he targets to minimize casualties. If they are Japanese or Vikings, wait for one more or better yet just keep them walled off while attacking their base. Switching into Archers are also always a option. If you are too late to realise he's going for Men-At-Arms and they're already in your base, make some quick-walls securing your resources coming in. Try not to panic and think critically, making smart walls potentially trapping your opponent forcing him into your town center. If you have a scout or other units near his base, you can try dragging his attention to his base while you deal with his Men-At-Arms. If he's too stubborn you might get away with sniping a vil or two.

In Team Games a Men-At-Arms opening is pretty common from flanks, as it allows time and resources to wall while queuing up Militias and Feudaling.