by sigmazero13
First, I should point out there's apparently confusion in the German translation. There are two different effects: "Rout", which means you lay down your units, and "retreat", which means the units leave the area completely. Most of the time, a unit that "retreats" is also "routed". In the German translation, apparently is uses the same word for both terms, though.Anyway, I think the example you are giving is referring to the "rout".
When you are forced to rout a unit, you must rout an UNDAMAGED unit first, if possible. You can only rout a damaged unit if all the undamaged units are either routed already, or dead.
So in your example, in the second round, Pegasus Rider 2 must be routed, and Pegasus Rider 1 must take the second damage (as you must always apply damage to a unit that's already damaged first).
I hope this helps.