Why Aba Al-Fadl Al-Abbas (peace be upon him) is called "The Lion of the Bridge" [Sab' Al-Qantarah]?

Aba Al-Fadl Al-Abbas (peace be upon him) has grew up in an environment that enlighten the path for the mankind. And in his childhood and youth, he witnessed the battle between right and falsehood, light and dark, and where the virtue was always the winner.

He (peace be upon him) embodied the ideal of genius, as he was the disciple of four of the infallible Imams; his father, brothers Al-Hassan and Al-Hussayn and his nephew Ali Ibnu Al-Hussayn (peace be upon him).

He (peace be upon him) has many titles and nicknames, some came after his heroism in the battle of At-Taff, while others were given to him before that time, among which "The lion of the bridge [Sab' Al-Qantarah]" and some think that it meant the lion of Karbala or of the battlefield...

However, when the Commander of the Faithful (peace be upon him) came back from the battle of Siffeen, a group of those who were with him then retired. "Al-Khawarij" started inciting people to fight against him in every place they entered, until they reached Al-Nahrawan, and Abdullah Ibnu Al-Khabab Ibnu Al-Art was then the governor of the Commander of the Faithful (peace be upon him) on it.
They arrested him and asked: “What do you say about Ali Ibnu Abi Talib (peace be upon him)?” He answered: “What can I say about a man upon whom the Messenger of God has said: "Ali is for me like how was Aaron for Moses..." but good.” They said then: “God is the greatest! He has disbelieved,” and they killed him and they killed his pregnant wife, opened her belly and have extracted her foetus and slaughtered him on her chest on the Tigris River, so all their bloods have shed in its water.
When the Commander of the Faithful (peace be upon him) heard that, he gave a speech, mourned Abdullah Ibnu Al-Khabab and said: "No sitting after the killing of the good servant Abdullah Ibnu Al-Khabab."

Imam Ali (peace be upon him) made ready his army and started walking towards the city of Al-Nahrawan. When Al-Khawarij heard that, they closed all the gates and barricaded themselves inside it. The Imam (peace be upon him) raised then his voice and preached, he warned them from sedition, reminded them of the true religion, and gave them advice and homily. Some of them retired from fighting against him, while the rest insisted and declared stubbornness. So, the Imam (peace be upon him) was determined to fight them and said: only me and my sons would fight, and he gave the command of each of the four gates of the city of Al-Nahrawan to his sons, the eastern gate to Al-Hassan (peace be upon him), the western gate to Al-Hussayn (peace be upon him), the northern gate to his son Mohammed Ibnu Al-Hanafiyyah, and he (peace be upon him) was heading towards the middle of the city, when he (peace be upon him) felt someone behind him, it was his son Al-Abbas, who was then only 14 years old, he (peace be upon him) asked him: “What are you doing here, O son Abbas?” Al-Abbas then asked him: “Why, O commander of the Faithful you gave the command of the gates to each of my brothers, there is no gate for me?” The imam (peace be upon him) told him: “You are young, O Son!” Al-Abbas replied: “Did you not fight along with the Messenger of God while being young, O Commander of the Faithful?” The Imam (peace be upon him) then told him: “But only the Gate of the Bridge "Al-Qantarah" remains.” Al-Abbas said: “I'm for it and it is for me, O Commander of the Faithful!”
The narrator said that he rejoiced and went happy towards the said gate. Imam Ali (peace be upon him) started fighting, but whenever he shouted his known anger shout, they would escape. Abdullah Ibnu Hazem Al-Khariji has said: “When we heard the anger shout of Ali, we thought that the walls were answering him, so we ran away, and when we arrived to the eastern gate, we found Al-Hassan there. Once he saw us, he attacked us saying: “How can you seek to escape from my side and I am the son of the Commander of the Faithful?”
We run then towards the western gate, so Al-Hussayn attacked us saying: “How can you seek to escape from my side and I am the son of the Master of the guardians?” We then run away to the northern gate, a brown boy attacked us saying: “I'm the son of the Leader of the Resplendent!” When I asked about him, they informed me that he was Mohammed Ibnu Al-Hanafiyyah.
So, we all said: “Let's escape from the swords of Ali and his sons from the Gate of the bridge.” When we have reached the bridge, we found a young boy on his knees and his eyes were full of anger. He has a sword in one hand and taking a horse with the other one, he attacked us saying: “How can you seek to escape from my side and I am the son of the Red Death, I am the son of Ali?” And then, we could only see flying heads and scattered bodies, and he kept fighting until his sword was broken, he then started throwing the soldiers even those on horses in the river.
His father Ali then came and saw him sitting on the ground with their heads next to him, he kissed him on his forehead, carried him and put him on his chest smiling and said: “God bless you, O my son, I am sparing you for a greater day than this one.” Al-Abbas (peace be upon him) replied: “I will then enchant you, and I'm your son!” The Imam (peace be upon him) told him: "You are apt and generous!"

Peace, mercy and God's blessings be upon You, O master, O Lion of the Bridge, O Aba Al-Fadl Al-Abbas!