How to Control the Gap
Gap control is one of the trickier decisions you will have to make when playing defense. The 'Gap' refers to the amount of space between you and an opposing player entering your defensive zone with the puck - usually a one-on-one.
The first step in controlling the gap in to skate backwards at the same speed as the oncoming forward. The is definitely no easy task. If the forward with the puck started his rush deep in his own end, I will start skating forwards hard towards my own net, then turn to face the forward skating backwards to make sure I have enough speed.
While you're still in the neutral zone, your gap can be fairly wide (maybe two stick lengths) as the forward still has a lot of options as to where he will skate, and what he'll do with the puck. Once he reaches the blue line, you've got to narrow the gap to put some pressure of the forward.
Your goal in a one-on-one situation is to push the forward to the outside lane. If you leave a gap too wide, you allow the forward to easily move to the center of the ice, where he has a better chance to score.
Be careful not to close the gap too early and over-commit to checking the forward. If he's able to deke you, and get around you, he'll have plenty of ice left to go one-on-one against your goalie.
The key to gap control is to keep enough space to make the forward's option to beet you on the outside look as attractive as possible, while still giving yourself a chance to force him into the corner if he takes that route.
Some players will leave too much gap once they realize the oncoming forward is a faster skater than them. While your speed will change with a faster skater, your strategy should remain the same. You still want to encourage him to go to the outside. Your goalie will always have a better chance of stopping a puck from the wing than in the slot.
Related Tip on Controlling the Gap:
How to Play Defense One-on-One