Leadership of the patarini passed to a man named Arialdo of Carimate.  Realizing that he needed more than moral authority to deal with Guido, Arialdo decided to enlist the services of someone who was skilled in the use of force.
 
He found such a man in Landolfo’s brother, Erlembaldo Cotta.  Erlembaldo was a seasoned military commander who was also deeply pious.  During the years in which he plied his trade, he had undoubtedly seen—and engaged in—more than his share of killing.   By the time Arialdo approached him, he had already laid down his sword in favor of a just-completed pilgrimage to the Holy Land, and he was planning to enter a monastery.
 
Arialdo persuaded him to devote himself to service of a different kind.

The task ahead of him was not an easy one, since Milan’s feudal overlords were aligned with Guido, and they held a near-monopoly on weapons, armor, horses, and all the other significant components of physical force.

Somehow, though, Erlembaldo was able to train unskilled commoners to not only stand up to armored knights, but defeat them.

I suspect that he may have taught them some of the tactics of modern-day guerilla warfare, in which they would assemble quickly for a battle, then melt back just as quickly into the everyday civilian population they were part of.  In addition, I wouldn’t be surprised to learn that they attacked the feudal overlords in their own homes, where there were only a few of them, and before they’d had a chance to get into their armor or onto their horses.
 
I also have mental images of Erlembaldo’s troops possibly dropping heavy nets like the ones Roman gladiators in the Colosseum used, but now thrown from the rooftops onto their mounted foes, ensnarling and disorienting them—possibly even bringing them to the ground, if enough citizens surrounding them pulled down on the nets.
 
This is all speculation, however.  What’s factual is that these citizen-soldiers proved to be a surprisingly effective fighting force which caught the old power structure completely off guard.  

With the backing of Pope Alexander II, Erlembaldo began by deposing key abbots, then moved against Guido himself.  On Erlembaldo and Arialdo’s recommendation, the pope excommunicated Guido.

Rather than accept this judgment, Guido sent men to ambush Arialdo.  They brought him to an island in Lake Maggiore, where a pair of priests went to work torturing him.  They mutilated his right hand, feet, and genitals;  gouged out his eyes;  and cut off his ears, tongue, and nose, then stuffed them down his throat.  Finally they killed him, and dumped his weighted body into the lake.  

More battles ensued, and the stakes grew higher.  At one point, Erlembaldo found himself in a position where he had no ethical choice but to flatly and openly defy an enraged Holy Roman Emperor who was on the verge of sending in his own army.  

But in the end, Erlembaldo won the day, replacing Guido with a young man who appears to have been the son of one of the pataria reformers whom the Milanese clergy had recommended for the job many years before.

Erlembaldo’s victory affected more than just the church.  The feudal overlords’ iron grip on Milan was also broken, giving the common people expanded freedoms. The city thrived.