Elza e Fugie is a generic defensive technique that utilises the false edge parry, followed by a riposte as you slip back out of measure. Marrozo gives us an excellent description in Libro 1, Capitolo 14 of his text…

In case you don't know what elza e fugie is, I will explain it to you presently. Elza e fugie is when your opponent delivers you a dangerous blow as you are in porta di ferro alta or stretta or larga, or sopra il braccio, or in coda lunga e stretta, or in cinghiara porta di ferro ­ no matter what posture you are in, as long as it is a low guard. In the time that he delivers the blow, you will give a strong upward falso followed by a mandritto fendente, at the same time pulling your right leg behind the left. This is called elza e fugie. Please know that this technique is a good counter against one who wants to penetrate your guard therefore make a note of it and be careful. (William Wilson,  Arte dell’ Armi Books One & Two, http://www.marozzo.org/marozzo­trans.pdf, accessed 27 Feb 2007)

The actual technique generally works as follows:

1. From our low guardia, parry the opponent's attack with a rising falso (either falso manco or falso dritto). The opponent’s sword should be beaten offline, and our sword should be in the high line.
2. Using the charity ribbon technique to conserve momentum, riposte with a descending blow to an open target on the opponent. Head and arms are both excellent targets. This riposte is made as you slip back the front foot to the rear foot.
3. Step back with the rear foot into a passo largo stance. This should add a slicing action to the riposte, as well as helping us to fly back out of measure.
4. Ensure you finish in a guardia with the sword in prescence.

So lets look at a couple of examples from Manciolino, to see how this would work. We'll start with the defence of the mandritto from Porta di Ferro Larga…

From Porta di Ferro Larga, when the enemy throws a mandritto to the head, parry with the false edge and riposte with a mandritto to the face. [Manciolino, Libro 1, Capitolo 18]

This is another of those techniques where he gives us a specific action, but omits the footwork. If we perform this defence using the principles of elza e fugie it quickly becomes a readily understood and effective response. So when we look at it step by step it becomes…

1. Our guardia is Porta di Ferro Larga, and our opponent has taken the initiative and thrown a mandritto at our head.
2. Without moving our feet we parry the incoming blow with a falso dritto,  ensuring we lead with the tip. We use the falso dritto since this lets us cut into the inside of the opponent's blade, deflecting it to the outside of our buckler.
3. At the top the arc for a rising cut we allow the sword to loop over, and come back down with a mandritto to the opponent's head. We also slip back our right foot to the left as the blow is descending, which should result in the debole of the sword cutting the opponent's face.
4. For our safety, we then step back with the left foot, pulling the blade edge through the face with a slice, finishing in Porta di Ferro Stretta.

Next we'll look at the defence of the mandritto from Porta di Ferro Stretta. This sequence is interesting for us because we don't know which side of the sword the mandritto will be on, and hence we have two possible variations.

From Porta di Ferro Stretta, as they throw the mandritto to the head parry with a falso and cut to the leg with a riverso. (Manciolino, Libro 1 Capitolo 6)

For the purposes of  illustration, we are going to assume both fencers are starting from Porta di Ferro Stretta, and that the attacking opponent is using the extension into Guardia di Testa as the charging action. Thus we have the mandritto cutting either over the top of our sword, or underneath our sword by cut over. Let's start with the mandritto as the direct cut over our sword.

1. The opponent extends to Guardia di Testa, and the throws a mandritto to the head on a left pass.
2. Parry the mandritto with a falso manco by extending into Guardia di Faccia, pointing the sword at the opponent's left shoulder. This action should be done on a slip back with the right foot.
3. Continue the momentum of the sword by rotating the forearm to turn the sword, and then throw a riverso to the leg as you step back with the left foot into a passo largo stance.
4. For your safety slip back the right foot, extending the sword into Guardia di Faccia. Retreat back out of measure and then return to Porta di Ferro Stretta.

We want to slip back on the parry in this case to give ourselves time to react to the attack.

Now let's look at the mandritto variant thrown by cut over.

1. The opponent extend to Guardia di Testa whilst gathering the left foot to the right, and then on a right passing step throws a mandritto to the head.
2. Parry the mandritto with a falso dritto that transitions to Sotto il Braccio, whilst slipping back the right foot.
3. Continue the momentum of the sword, pulling the sword tip past the tip of the opponent's sword and then cutting riverso to the opponent's leg as you step back with the left foot into a passo largo stance.
4. For your safety slip back the right foot, extending the sword into Guardia di Faccia. Retreat back out of measure and then return to Porta di Ferro Stretta.

Again, we slip back with the parry to give ourselves time for reacting with the parry. In both cases the slip is slightly increasing measure, and thus extending the tempo of the attack from our opponent.