There are, in martial arts, two broad categories of styles; grappling and striking. Striking arts rely on transference of force through impact by using appendages to bludgeon opponents into submission or unconsciousness. Grappling arts aim to throw, pin, or submit the opponent via strangulation or joint locks. These two broad styles are found in various levels of purity such as the exclusive styles of boxing, judo, BJJ, Muay Thai, Shuai Jiao, and many others. They are also found in mixed styles in various portion and use such as in Japanese jujitsu, MMA, Wing Chun, other types of kung fu, and many of the Silat styles.
In the mixed styles grappling is used in many ways and to many purposes depending on context. In most cultures for example wrestling which included ground fighting would tend to be reserved as exercise, sport, and for use in heavily armoured combat such as in medieval plate armour. Wrestling outside of heavily armoured fighting tended to include either limited ground-fighting or none at all. Judo's predilection toward heavily scoring ippon (throws) is a throwback to this. This type or grappling tends to be fast and designed to remove the opponent's balance and/or their grip on you as fast as possible.
Geoff Thompson makes great distinction between self defence and match fighting which is single combat over a more extended timeframe. This is incredibly helpful in understanding the form of grappling in these systems and why grappling or rather certain kinds of grappling can actually be a negative component in self defence.
As I discussed earlier most grappling in fighting systems before the age of gunpowder were designed to keep you standing and put the opponent down. A downed adversary could be picked off relatively easily with a spear or sword and even trampled by horses or other soldiers. Many of these systems also included standing jointlocks such as jujitsu or chin-na.
This principle of not getting tied up with an opponent is incredibly relevant for self defence. The risk of being stomped or struck while standing by your adversary’s allies is a real threat. Entanglement prevents your ability to escape, evade, and attack effectively when you need to be mobile. The ground grappling in the US military’s various empty handed combat systems are based on the idea of detaining the enemy until friendly forces show up to retrain, shoot, or skewer them. Most highly trained grapplers who are honest about their skill will tell you that the ground is the place you least want to be during a self defence scenario.
As I said a downed opponent could be finished fairly easily by spear or by sword. Unfortunately the presence of weapons can be a major detractor when it comes to grappling. Weapons like knives make remaining close to an adversary a major hazard. Positions where it is safe to control while grappling empty handed become even less safe while trying to control someone who is equipped to stab or cut you. You do not want to get tied up either standing or on the ground with someone who has a weapon.
You resort to your training
People have a tendency to fall back on what they practice most. While in theory it is great to say that the ground is not where you want to be, if you regularly include techniques and training which entangle you with your opponent you are likely to fall back on that training under stress.
Some grappling styles also include submission moves which, again depending on context, could be considered excessive force. Strangulation, that is chokes, are banned by most law enforcement agencies in the US and Canada, being seen as risky and potentially lethal. Most joint locks if carried to conclusion could potentially maim an attacker meaning legal ramifications for the snapper of arms and legs. Some joint locks are what the Japanese call “ara waza;” severe technique. These fast and brutal breaks have no option for submission.
“But the Gracies said 90% of fights go to the ground. Doesn’t that make grappling the best?”
That figure is probably more like 99%. The truth is that most of those people are not trained strikers with good footwork, posture, and ring control. Most people getting into match fights are not professional fighters, amateur fighters, or even your martial arts hobbyists. Change that to a self defence scenario in a crowded bar or nightclub and ask yourself if holding on to someone either standing or on the ground is where you’d like to be and how you can most quickly dispatch someone. When it comes down to it a hard punch and good footwork are the best ways to achieve your goals.
Now with all of this criticism levied against much of grappling why would I still recommend people train it? Well it can be great for things like; being able to stay on your feet, breaking grips, weapon retention, and building a good structural foundation for striking. Some types of grappling which avoid body to body contact and emphasize joint locks can be even less entangling. Grappling is amazing but you have to keep in mind where it fits in self defence if you want to focus on high percentage, broad context, fight ending skills.