Less than 10 percent of the world’s people, and of the participants in combat sports worldwide, are left-handed. However, a majority of top-level competitors in combat sports worldwide are left-handed.

The number of left-handers account for less than 10% in combat sport, yet they manage to be at the top-level in sports. How?

Which of the following, if true, most helps to resolve the discrepancy presented in the passage?

1) Left-handedness is more common in primitive cultures with high rates of death by violence than in other primitive cultures.
Out of scope. Statistics about the primitive cultures is not going to help.

2) Among top-level competitors in many non-combat sports, such as tennis and baseball, left-handedness is also much more common than in the general population.
Out of scope again. It is just a fact about NON-combat sport. We can't correlate.

3) In many cultures, children are discouraged from performing tasks with their left hands, even if the left hand is their dominant hand.
This may give us a reason why left-handed population is so less. But, gives no reason behind their dexterity OR winning disposition.

4) Because left-handedness is so rare, opponents of left-handed fighters are ill equipped to handle the positions and angles from which those fighters attack.
This gives us a perfect reason how left-handed people can use their opponents' limitation in defending left-handers' blows. For the very reason, the chances of left-handers becoming victorious are more.
Correct.

5) A significant number of left-handed competitors in combat sports have trained under coaches who have forced them to fight from right-handed positions and angles.
This goes into the nitty-gritty of the sport itself. How do we know that fighting from right-handed positions can be advantageous. Also, merely forcing someone to do something is no guarantee that the person will acquire the skill to such a degree as to become victorious and to be the top-level.