Boxers always perform some moves then guard back and most of them are slow regarding top boxers, why don't they perform fast consecutive punches, is it bad idea or don't they have enough stamina to perform continuous punches?
Punching is both advantageous because it can potentially hurt your opponent and risky at the same time (at the moment, I can think of two reasons for it being risky).
Boxing matches are oftentimes very dependent on stamina (of course, for nearly all sports - but boxers occasionally simply fall from exhaustion rather than a KO) so boxers want to conserve their energy and really only hit when it's low-risk, high-reward as much as possible. Stamina also comes into mental strength as well. Being very tiresome not only slows you down physically, but makes it harder to anticipate and react quickly to your opponent's movement. Secondly, one arm extended to hit the opponent is one less arm to defend. If the opponent manages to dodge your attempt to hit them, that's much easier for them to hit you now - as you only have one arm now to both anticipate the next blow - and actually defend yourself against it.
Since it's very possible for a.) A boxer to get KO'd in the beginning of the match and b.) For the match to be extremely long and physically tiring for both opponents - boxers have to optimize everything - how much they move around, when to defend, and most importantly, when to punch.
I was a boxerin one of the toughest gyms in the country for one of the best trainers in the country. I can sum up your answer -
Because your opponent moves.
- Every time you throw a punch you are leaving a zone open to get hit.
- Every time you throw a punch you are potentially losing balance, you simply can't keep throwing punches if you are off balance or opponent is backing up. It is almost impossible to throw more than 3-4 punches without losing balance. Either your opponent is terrible or he will move and you will lose balance.
- The only way for you to safely throw a punch (with lower change of getting hit) is throwing your jab. Your jab can only be thrown so quick.
- When you jab you can keep your body turned. When you throw a flurry of punches you have to square up and you will be countered more.
- You can miss. A missed punch is about the worst thing that can happen in a fight. It hurts, it wears you down, and you are wide wide open for 2 seconds.
There is absolutely nothing wrong with just punching and punching as long as you can land your punches and opponent isn't hitting you too much. Your tiredness from punching and landing is far less than the effect of getting punched if well conditioned.
I will reference Jedo's answer. He was on the right track, but missed the point.
A simple answer is to say that if a boxer punched continuously throughout the round for 10-12 rounds, he would become tired and not be able to stand in a defensive position. Therefore, the other boxer would only need to successfully defend these punches to wait him out.
Since a boxer cannot punch for 30-36 minutes straight, he needs to optimize when to punch. Jedo mentioned low-risk, high-reward. These punches both need to find sweet spots (head shots, gut shots) all the while ensuring he does not leave himself open for a counterattack.
A good boxer will feint with low-energy punches to set up shots in the sweet spots. Once an opportunity becomes clear (a temple, or a jaw, or the solar plexus), boxers will punch with their whole body.