In karate, more strikes and kicks are used - ´fighting takes place over a longer distance, the strength and speed of the fighter is built against the strength and speed of the enemy. Judo, on the other hand, makes more use of possession (immobility, prying, strangulation) and the warrior tries to use the opponent's "clumsiness" against himself. It doesn't matter when it comes to sports - so let your son choose according to "taste". When it comes to self-defense, I recommend smaller and lighter individuals rather karate (defense takes place at a distance, so it does not allow a heavier / stronger opponent to simply "lie" to the attacker). Inco-self-defense is always "less aggressive" than competition or attack. ;-) And yes - judo is based on balance and the use of adversary mistakes. But there is a difference in self-defense training (against a similarly disposed ´augar´) and its real use (when you do not choose an attacker) - and I have tried that a sufficiently determined attacker does not have a general problem with a much weaker person - judoka, a friend once explained to me, that she's not afraid of being attacked because she's doing judo - but she weighed about half of what I did - she didn't stand a chance, just a 50-pound girl meter guy - if she "reaches" her, lies down and immobilizes). The karateka has the advantage that he uses his art from a greater distance and with a suitable blow or kick will neutralize almost anyone. Nothing against judo. ;-)