Closing the Range
Closing the range (gap) between you and your opponent is possibly the toughest part of sparring, but is one of the most important parts. If you are not in range, you cannot score. The more time you are in range, the greater your chances of scoring.
Most people try to close the gap with a great burst of speed or they let the opponent close and then try to counter the attack. However, charging requires explosive power in the legs and counter fighting gives the initiative to the other fighter. Another way to close the gap is to use inertia to your advantage and to recognize when it is being used against you. Inertia, as you may recall from science class, is the tendency of an object in motion to remain in motion and an object at rest to remain at rest.
As discussed above, sparring opponents try to maintain a comfort zone between themselves. This is the distance at which they think they may safely detect and defend any attack. The width of this gap depends on the physical reach of the opponent and his/her preferred method of fighting. For instance, taller fighters and kickers tend to stay further away so they can use their reach. Smaller fighters and punchers like to fight in close to compensate for their lack of reach. If you close at a specific speed, your opponent will back away at an equal speed to maintain his/her comfort zone. To use inertia to close the gap, you need to take advantage of this tendency to maintain a comfort zone.