Most fights are decided by punches to the head
In a fight, most people strike toward the face. It seems to be embedded in our genes. As stated above, the one who land the first good punch usually wins. That first good punch will probably be to the head. However, punches to the head have two big problems: the head is very mobile and difficult to hit, and, since the head is dense, punching it with the fist will probably break the hand.
Most fights are at close range
When sparring, competitors usually start outside of kicking range. Then the competitors will close the range, attack, and then open the range again. However, fights usually start at punching range and rarely, if ever, have the back and forth motion seen during sparring matches. Usually, a few punches will be thrown and then the fighter will clinch, fall to the floor, and start grappling.
Opponent is very unlikely to use martial arts techniques
Since most martial artists train to be non-violent, most will not be initiating fights. Since martial art training involves discipline and hard work, most violent people are weeded out. Therefore, it is highly unlikely that attackers will use martial arts techniques. Not impossible, just unlikely. However, they may use highly effective street techniques that have been learned through hard experience.