... Is there any guy/girl in the world that can throw a Kamehameha at your face? I doubt it very much, is it possible? Well.. Yeah... I guess, I don't understand how the universe works and I doubt that anyone does so everything is possible.
As far as I understood the nature of Kamehameha, it is similar to Fireball, may be Electricity. So it is about controlling Elements (Fire, Water, Earth, Air). Controlling Elements is definitely possible (but it is not very energy efficient, like said before).
There is a movie out (Flarsky, Long Shot) with the subtitle "Unlikely, but not impossible ".
The thing is, mages and sorcerers in our world are not keen on having much attention and making shows (only few exceptions). They like to work unseen and invisible.
An evil mage e.g. creates an invisible pipe and drains the energy of his victim. Slowly, this can lead to death, if there is no strong defense or help.
Positive mages: There was a Tai Chi master fighting against two full contact Karate masters simultaneously. Before the 2 attackers reached the Tai Chi master, they fell down and the fight came to the end. There was no physical contact at all.
A rough form of defense is
to let the attacking energy reflect back to the source. So the evil doer gets a taste of his own acting (and gets damage).
A young woman in India sitting on the ground. Two attackers with knives ran to her to kill her. On half way, they fell down, got a heart attack and had to be delivered to the hospital.
Their own hardened heart almost killed them.
The highest form of "self defense" is like the following.
The founder of Aikido (Morihei Ueshiba) mentioned:
"when one truely radiates unconditional love, no thought of attack can consist in his surroundings."
May be he himself got to this point. Other Aikido ppl still have to do physical defense I guess.