Generally speaking targets of choice IMHO (roughly in order):

- knee (easy to hit, easy to break)

- shin (if the person is standing on that leg it's easy to break)

- ribs, breast bone, collar bone (big huge target that is hard to move out of the way. Ribs are easy to break. A collar bone break will effectively stop an opponent from using their arms, though it is hard to hit)

- neck (hard to hit but if you miss you've got collar bone and jaw as backup. Some fighters handily give you their jaw to protect their neck. If you hit the neck with a clean shot, there will be no fight...)

- head (hard to hit, but you can break it in two with a clean shot... seriously).

You will notice that all of my targets of choice other than neck are bones. Soft tissues are not a good choice for a striker because they absorb damage too easily. Also, they don't incapacitate the opponent immediately. Often the person can go for a good 10 seconds before they even realize that they are damaged.

Furthermore groin and eyes are very hard to hit. The groin is easy to protect and the eyes are just too small. You could hit them against an untrained fighter, but you can do just about anything against an untrained fighter.

You will also notice that apart from the head and ribs, none of these are targets that are used often in sports matches. It's obvious why. If a sports fighter walks out, notices that his opponent's leading leg is too straight and breaks the knee on purpose... well that person isn't going to get invited back to most tournaments.

Also most sports fighters put too much power into their strikes. If you actuate your muscles all through the strike, it slows it down. Rather than thinking about powering through an opponent, they would do better to think of their limbs as whips. You accelerate quickly, using every joint as a way to multiply the speed. When you hit, you then need to align your bones so that the rebound force is directed along the longitudinal axis of the bones. Each bone must be aligned in an arch leading to the ground so that you take the brunt of the force through your skeleton not through your muscles.

It takes a long time to master this technique (and I have not done so ;-) ). One of my instructors could break the ribs of his opponents with kicks even though we wore padded fibreglass armour. We also wore plexiglass helmets. The people who first started using these (one generation before me) sometimes broke them into pieces while sparring so a rule was implemented to tell people to be careful when hitting the head ;-)

Like I said, I don't really know how far you would get against a well trained ground fighter who is good at avoiding getting hit badly. I think the odds are in favour of the ground fighter winning the fight if they don't make any mistakes, but it would be very dangerous against a good striker.

I'm sure there are lots of people who think the above is complete poppycock ;-) In fact, it is testament to HN etiquette than someone hasn't said so up to this point. For me these days it is occasionally fun to think about this stuff, but I have been "retired" from karate for nearly a decade now. Hope someone will find it interesting even if they don't agree ;-)