Is Boxing Haram?
Question

Allah has given me the gift of being a good boxer and I am confident that I can become world champion in the next few years. I have had a successful amateur boxing career and am about to start a professional boxing career. 
I have recently come into deen and would like you to inform me whether I am allowed to do professional boxing or not. 
While boxing I feel that I could do a lot of good for Islam and help Muslims by both speaking about Islam (in order to encourage in particular the youth to go on the right path (Islam) and giving money to charity etc.
It is my intention eventually to perform Jihad of the body one day and that my years of training as a boxer would eventually serve for this purpose.
Please could you give me evidence in support of your fatwa. (P.S. I would not be competing against Muslim brothers only against non-Muslims).
Praise be to Allah.Physical strength is a blessing from Allah 
We praise Allah for guiding the brother who asked this question, and we ask Allah to make him steadfast in his religion. And we praise Him for giving you physical strength, in which there is a great deal of good for you and for the Muslims in sha Allah, because the Muslims strengthen and support one another. 
Physical strength is a blessing from Allah and a gift from Him which He bestows upon whomsoever He wills and withholds from whomsoever He wills.  
The Messenger (peace and blessings of Allah be upon him) preferred a strong believer to a weak one; this includes both strength of faith and physical strength.
Abu Hurayrah said: The Messenger of Allah (peace and blessings of Allah be upon him) said: “The strong believer is better and more beloved to Allah than the weak believer, although both are good. Strive to do that which will benefit you and seek the help of Allah. Do not feel helpless and if anything befalls you, do not say ‘If only I had done such and such.’ Rather say, ‘Qadar Allah wa ma sha-a kan (The decree of Allah and whatever He wills happens).’ For (the words) ‘If only’ open the door to the Shaytan.” (Narrated by Muslim, 2664) 
Ruling on sports in Islam
It is very good for the believer to engage in permissible sports so that he will be physically strong and will preserve his health, which will help him to do acts of worship and strive in jihad for the sake of Allah. 
The Messenger (peace and blessings of Allah be upon him) praised good health and even regarded it as more important than money. 
It was narrated from Mu'adh ibn ‘Abd-Allah ibn Khubayb from his father that his paternal uncle said: “We were sitting in a gathering when the Messenger of Allah (peace and blessings of Allah be upon him) came, with traces of water on his head. One of us said, ‘We see that you appear to be in high spirits today.’ He said, ‘Yes, praise be to Allah.’ Then the people spoke about riches. He said, ‘There is nothing wrong with riches for one who fears Allah, but good health is better for one who fears Allah than riches, and being in good spirits is a blessing.’” (Narrated by Ibn Majah, 2141; Ahmad, 22076. This hadith was classed as sahih by al-Albani in Sahih Ibn Majah, no. 1741) 
Aims of playing sports in Islam
The Muslim’s aim in playing sports should be to strengthen himself to do acts of worship and to support the religion of Allah, to defend His sacred limits and to protect the honour of the Muslims. 
If that is not the case, then at the very least he should aim to earn himself a living in this world, protect himself from enemies or use his physical strength to earn a living, so that it will be a means of him eating from what he earns with his own hands. 
Al-Miqdam (may Allah be pleased with him) narrated that the Prophet (peace and blessings of Allah be upon him) said: “No man eats better food than the one who earns it with his own hands. The Prophet of Allah Dawud (peace be upon him) used to eat from what he earned with his own hands. (Narrated by al-Bukhari, 1966) 
Abu Hurayrah (may Allah be pleased with him) said: The Messenger of Allah (peace and blessings of Allah be upon him) said: “For one of you to chop wood and carry it on his back is better for him than asking (begging) from anyone who will either give him something or refuse to give him anything.” (Narrated by al-Bukhari, 1968; Muslim, 1042)
Is boxing haram?
This is with regard to permissible kinds of sports. But from what we see nowadays, most sports have gone beyond that and are no longer permissible; they have become haram, especially boxing which is the worst of sports, for the following reasons: 

It involves attacking the face, and the Prophet (peace and blessings of Allah be upon him) said: “If any one of you has a fight with his brother, let him avoid the face.” (Al-Bukhari, 2560; Muslim, 2612). This game is based on hitting the face of one's opponent with the strongest blow the boxer can muster. 
It is a waste of time. Allah has bestowed many blessings upon the Muslim, and He will question him about them on the Day of Resurrection. But people think little of these blessings and waste many of them such as good health and free time. One of the things that Allah will question the Muslim about on the Day when he meets Him will be his youth and what he did with it, and his life and how he spent it. What will this man say who spent his youth and his life training to fight people and wrestle with them and box with them in order to gain a title or win a prize? 

Shaykh Ibn ‘Uthaymin said:
“If a person should not waste his money on things that are of no benefit, it is even more important that he not waste his time, because time is more precious than money, and because the fact that the young and the not-so-young waste their time on these sorts of games that are of no benefit to them is something that is very unfortunate and regrettable.” (Fatawa Islamiyyah, 4/435) 

It is a harmful sport which can lead to irreparable damage, and Allah has forbidden us to harm our bodies, which He has commanded us to preserve and protect. 

‘Ubadah ibn al-Samit narrated that the Messenger of Allah (peace and blessings of Allah be upon him) decreed that there should be no harm or reciprocation of harm. (Narrated by Ibn Majah, 2340; Ahmad, 21714; this hadith was classed as sahih by Imam Ahmad and al-Hakim, and as hasan by Ibn al-Salah) (See Khalasat al-Badr al-Munir, by Ibn al-Mulaqqin, 2/438)
Because of your practising this sport, you know that there are many boxers who have been permanently injured, especially with damage to the brain and nerves.  

It involves wasting money and wasting people’s time with something that is of no benefit. Instead of being wasted on this useless entertainment, that money could have been spent on charitable causes. How many millions are wasted that could have been spent on feeding the hungry, building a mosque, opening a school or other good works? 
These sports – including boxing – have become an excuse for tribalism and nationalism. Sport, as it exists nowadays, has divided people and made people love or hate one another on the basis of the victory or defeat of a team.
It involves uncovering the ‘awrah, even if you do not do that, your opponent will. The man's ‘awrah is from the navel to the knee, as was narrated from the Prophet (peace and blessings of Allah be upon him). 

Similarly, it involves uncovering of the spectators’ ‘awrahs, both men and women. This is something that you cannot ward off or even denounce them for.
You say in your question that you will not fight Muslims, but will the people who organize the matches allow you that? I don’t think so, and you know better than we do. 
Boxing for Islam: Possible?
These fights are not held for the sake of religion, and they are not based on that. When people watch a fight, they do not think that this is a fight between Islam and disbelief. 
Moreover, when you fight, you will be fighting in the name of the country where you live, or which has given you its nationality; they will not allow you to fight in the name of Islam. 
And even if your opponent is a disbeliever, he may be from among the people with whom there is peace (ahl al-silm), not those who are in a state of war with the Muslims (ahl al-harb), so what right do you have to raise your hand against a man who is at peace with us? 
In conclusion, this sport is one of the haraam games that causes more harm than good. 
Boxing for jihad
With regard to your saying that you intend to go for jihad one day. 
These are beautiful words, even if boxing is haram. You can strengthen your body by doing other sports that are not haram. 
And Allah knows best.