Chapter 36- Scorched Earth

[LiamKerrington]

4) The ambush on the road heading towards the arena; where Bricks disarmed Number 5. (How did they know about the arena anyway? What made them take the initiative to attack it?)

To answer your question, Sir:
4) It is a good question, how they did know about the arena and what made them (aka The Mallers) attack the arena.

Editing = Rephrasing:

How did they know about the arena?

From The Kalani-Backstory we actually know that The Mallers were in a very advanced position compared with The Tower and probably CJ's Tower. They already had a huge map in work, and they had their scavenging. Thus they would know, where the zeehs would be encountered much more likely - meaning: the will have pinpointed the Arena as Hotel California; and actually I would even guess they'd known about the Devil's Workshop or the Hospital as kind of a hotspot as well. That was very early in the zeeh-pocalypse.
Considering the way they attacked the Arena with tanker trucks, and relating the whole side-plot with Lizzy, Saul, and Burt going for the petrol-store and the truck, it makes perfectly sense that Scratch and Latch considered the truck 'theirs', which was 'stolen' by Lizzy, Saul and Burt - simply because the truck already had its purpose. Leading to question part two:

Why would they attack the zeehs?

They had the means, the will, and actually a/ the strategy to do so - until The Towerites interfered and 'stole' a truck. But regardless of that: even The Mallers were humans after all, all evil and beasty scavengers and a rat pack Mad-Max-style - and yet still humans; and they probably just followed the simple strategy of surviving with the best defense available: "Attack 'em mofus!"

That's how I piece things together. Does this answer your question, WD?