Regarding Engaging in Dangerous Activities for Fun and Sport…
The Messenger of Allah (blessings and peace of Allah be upon him) said: “If a person spends the night on a roof which has no surrounding wall, and falls down and dies, no one is responsible for his death and if a person travels by sea when it is stormy and dies, no one is responsible for his death.” (Narrated by Imam Ahmad in his Musnad, 20224)
Ibn Battaal (may Allah have mercy on him) said: What it means, in sha Allah, is that he is no longer under the protection of sharee‘ah, because he brought his own destruction upon himself and he exposed himself to danger, and did not protected himself, so he is not protected by sharee‘ah, and no one could be regarded as not protected by sharee‘ah except in case of kufr. (Sharh al-Bukhaari, 5/89)
Al-Haafiz Ibn Hajar (may Allah have mercy on him) said: It is permissible when there is no risk. This is the well-known scholarly view. And if it is thought that it is most likely safe, then land and sea are regarded as the same. End quote. Fath al-Baari, 6/88
Shaykh Ibn ‘Uthaymeen was asked: Is it permissible to take risks or put oneself in danger, as we see nowadays in some kinds of extreme sports which may lead to the death of those who engage in them?
He replied: This is haraam. It is not permissible for a person to risk his life in doing things in which there is the fear of death or harm, because Allah says (interpretation of the meaning): “And do not kill yourselves (nor kill one another). Surely, Allaah is Most Merciful to you” [al-Nisa’ 4:29]. If Allah has forbidden that and said “And do not kill yourselves”, then anything that leads to death or leads to harm is also haraam. The Prophet (blessings and peace of Allah be upon him) said: “Your blood, your wealth and your honour are sacred to one another.” Just as it is not permissible for a person to transgress against others, it is not permissible for him to transgress against himself by exposing himself to that which may cause death or harm. End quote.
Fataawa Noor ‘ala al-Darb, 13/252
SUMMARY: The person who does this kind of action or takes this kind of risk, if it is for the purpose of training in modern methods of fighting in order to prepare strength against the enemy, there is nothing wrong with him doing that; rather it is enjoined in sha Allah, but the one who is in charge of that should choose those who are suited for this kind of mission and are physically and mentally prepared for it and able to do this kind of mission and train them properly before letting them embark on this kind of mission for real.
If he dies or is harmed by doing that, he is not killing himself; rather he will be rewarded for his intention and his action, in sha Allah.
As for doing it as a sport and for fun, as is common nowadays, it is not permissible.
And Allah knows best.