Related but Different
Kumite (sparring/fighting) and goshin (self protection) are not the same, but despite this seemingly obvious truth, many people constantly equate effectiveness in one with effectiveness in the other. In some ways, the two are certainly related to each other and have skills that support each other, but they take place under completely different circumstances against completely different opponents.
Modern competitive kumite in karate has developed into two main categories–point-fighting and knockdown fighting. If you watch sparring from nearly any style of karate, it will most likely geared toward one of these two competition platforms and, regardless of the style the practitioners study, most people in a given category will look very much the same while fighting. The reason for this is simple–the rules of each category dictate the tactics necessary to achieve victory.
In point-fighting, the rules require specific protective equipment (typically a cup, a mouthguard, headgear, hand pads and foot pads, but sometimes shin pads or chest protectors are also worn) and in order to win you have to strike your opponent (some styles do no-contact or light-contact, while others do full-contact) before they can strike you. This results in a reliance on pads to protect you and give you extra reach for your strikes, and it causes you to throw a lot of feints and explode into and back out of your attacks in order to be elusive.
In knockdown fighting, there is typically little or no protective equipment other than a cup and mouthguard (sometimes gloves or headgear are worn, depending on the style) and the goal is to knock your opponent down with strikes to the head or body that render them unable to continue. This results in a high level of mental and physical toughness and promotes a very aggressive fighting style. In some styles, hand strikes to the face are not allowed, which can sometimes cause fighters to leave their face open to be punched and promotes flurries of powerful punches to the body and close-range kicks to the head.
Neither of these competition rule sets is necessarily better or worse than the other, but they are not necessarily applicable to protecting yourself from harm outside of a competitive arena. In both, you are assured to be fighting one opponent who, most likely, has a similar skill set to you. In both, you are assured to be fighting on a stable floor in an arena of a known size and shape with no obstacles in it and good lighting. In both, you are assured to be trying to reach the same goal while following the same rules. In both, you are assured that there will be no weapons involved in the fight.
Physical self protection, unlike sparring/fighting, is something that is trained for but very rarely put into use. The most often used tools for protecting yourself from harm are situational awareness and common sense, which are not physical skills, and if you apply those properly you will tend to avoid most situations in which you would need to apply the physical skills you learn for self defense in karate. That does not mean, however, that those physical skills should be ignored or trained poorly.
In self defense, the goal should be to end a threat to yourself or your loved ones and those involved are fighting under two different rule sets–you are fighting under the rules laid out by state and federal law for self defense, and the people attacking you are fighting without any rules at all. In addition, you may be surrounded by other people or obstacles, and the ground may not be stable or it may be slick, or the lighting could be very poor.
This results in a totally different skill set from kumite because your goal is to either disengage from or incapacitate your attacker(s) so that you can escape, and you have to account for your environment while being able to utilize techniques that are not allowed under competitive rule sets. Suddenly stomping strikes to the knees, grabbing and striking the throat, gouging and striking the eyes, biting, scratching and pinching, slapping and pulling the ears, pulling hair, striking the back of the head and spine, kicking and kneeing the head of a downed opponent, and grabbing and striking the groin are all allowed. All of that, and no referee to stop the fight if you give up or get knocked out.
These differences do not necessarily mean that competitive fighting is useless for self defense, but they do mean that it is not ideal training for self defense. The biggest advantages of kumite for goshin come in the form of reaction time, speed, mental and physical toughness, and confidence. When you spar and fight competitively, you learn both how to throw effective strikes and how to take them, and that is a vital component to self defense. If you are afraid of being struck and don’t know how you will feel and react, then you will be in serious trouble when someone attacks you. Could someone who only trains for kumite defend themselves from an attacker? Certainly! But that does not mean that they are as well-prepared to do so as someone who trains for self defense. That is why it is important to train effectively and with a specific purpose in mind.
The actual fighting techniques that you use in kumite are rarely anything special–most of them can be found in almost every striking martial art in the world. If someone wanted to do nothing but competitively fight, they could be taught how to do so very quickly, but in order to protect yourself as efficiently as possible there is a wide array of techniques for trapping, controlling, locking and striking available in karate that are not used in kumite, and those can take much longer to learn and become skilled with. In order to make your training effective for self defense, you must drill bunkai with a resisting opponent and occasionally spar with self defense applications in mind instead of competition rules.
Self defense drills (typically in the form of bunkai) must utilize techniques that are effective and do not require fine motor control, and they must become natural. Most people start learning these drills against formalized attacks (eg. a karate-style lung punch) and practice them on opponents who do not resist them at all. This is fine, at first, but eventually you must practice the techniques with more and more resistance and against more realistic attacks.
Bunkai-based sparring is a way for you to practice your drills in a more “alive” setting. Instead of squaring off with your opponent and fighting each other under a fair rule set, try to make things more realistic. Set up the sparring so that one person does not know who they will be attacked by or how and have the attacker surprise them with any attack they want, as long as it is realistic. The defender must then end the threat and escape from the attacker using any of the techniques–both striking and grappling–at their disposal. Making contact is important for both parties to understand what the techniques feel like, but control must still be used to avoid injures.