Offense
In Wii Sports Boxing, you'll be using three basic types of punches: the jab, the hook and the uppercut. By holding the Wiimote in one hand and the nunchuck attachment in the other, you can control your left and right hands independently by throwing punches at the screen.
The jab is the simplest of the punches, consisting of a quick, straight strike to either your opponent's head or body. The jab is performed by throwing one of your arms straight forward and then pulling it back. The quicker the punch, the more damage you'll do. Although a predictable move, the jab is quick and can be used in combination. By throwing a second jab as soon as you've pulled back your first one, you can score significant damage on your opponent.
The hook is a punch that strikes your opponent in the side of his body or head, and can be more difficult to defend against. The right hook is performed by lowering your right hand and then bringing it up and to the left in a diagonal line, while a left-handed hook is up and to the right. This move is slower than the jab, but does a decent amount of damage, and is generally less predictable than a jab.
The uppercut is a strong upward punch to your opponent's jaw. It is performed by lowering one of the controllers and then quickly bringing it straight up. While a powerful and satisfying strike, the uppercut is both slow and unreliable, and should not be depended on too heavily.
Defense
There are two defensive moves in Wii Sports Boxing: blocking and dodging.
Blocking involves holding your gloves in front of either your face or body to stop incoming punches from landing. Hold both hands in front of your face to block punches to the head, or in front of your stomach to block body blows. Mastering the blocking controls can be a bit tricky, but it is a useful technique, especially when facing a reckless opponent.
Dodging involves leaning out of the way of your opponent's strikes. It is especially useful because, unlike blocking, you can throw punches from this position. It is performed by moving both controllers, together, to one side. This is a useful technique for getting out of the way of strikes, especially uppercuts, and puts you in the perfect position to make a counter-attack.
Strategy
Many people make the mistake of relying too heavily on the jab. Although a useful and versatile move, it does have its limits. Many players become dependent on this move because the first few rounds of the single-player game aren't very difficult. It isn't necessary to throw different punches, or to use defensive maneuvers. However, it is best to get in the habit of using other moves. You'll need them to defeat more difficult opponents.
Of course, there are also ways to use punches defensively. Because hooks are less likely to be blocked, throwing a hook to the body is a great way to get yourself out of a tight spot and force your opponent to back off.