This evening I was engaged in a street fight and I realized that he was a boxer because of his stance. His kicks were very weak, but he was pretty fast in punching and he was taller. I realized I could jump and kick better. I managed to land in several kicks and I got a punch in the right eye. By the way I am not a martial artist, but I like it and I am pretty fit and fast. Fortunately, the fight ended for good, but how can one best defend against a boxer with kicks (or other defenses)?
The subject of "puncher vs. kicker vs. wrestler" comes up a lot in martial arts. The general philosophy that's put forward is: "Don't box a boxer. Don't kick a kicker. Don't wrestle a wrestler."
The idea is that you don't want to fight someone on their terms. You need to take them out of their element, where they have no training and therefore become lost and confused and make mistakes that you can use against them.
In general, you perform the way you've trained. The more you train at a certain skill, the better you will be. The less you train at it, the worse you will be. And if you don't train at all at something, your performance will likely be very poor.
A boxer doesn't train with kicks or wrestling. A mostly pure kicker (Taekwondo style, for example) doesn't train realistically with the kinds of punches boxing does, nor do they train with wrestling. A wrestler doesn't train with striking at all.
So if you're fighting a boxer, you want to stick with techniques and strategies a boxer doesn't generally encounter during training. There are lots of these, because boxing is fairly limited in scope to a small number of punches and a small amount of footwork.
Make no mistake, though, boxers are formidable opponents, and it's because they train realistically, with partners that are hitting hard and fast and who want to win against them. They are very strong fighters in the scenarios that are familiar to them, and those scenarios are the ones commonly encountered in real fights (up close and in your face).
Furthermore, if you want to defeat a boxer, you need to train with boxers. Again, you perform the way you train. If you have no training with someone who uses boxing, you're setting yourself up for failure if you do end up fighting someone who's a boxer.
So make sure you get a boxer to train with.
With that understood, what are some of the things a boxer might not be familiar with?
1) Stay in the long range, on the outside. Boxers are best in the close to mid range, so you don't want to be there. They push forward until they can get close enough to land a good punch. In this range, kicking is ideal. The thing to watch out about, though, is that a boxer will rush forward while your kicking leg is still in the air. It takes time to kick and bring that leg back down, and that's time enough for a boxer to take the kick (or parry it) and push forward. You don't want to be make yourself vulnerable during a kick. Keep kicks low so you can recover your balance and react more quickly.
2) Keep moving quickly. Don't ever stay still, especially if he manages to get in close to you. Move your head up and down, left and right. Dip your body down and then up again. Step diagonally. Don't give him a target he can lock onto. You need to keep him thinking. As soon as you move, he has to recalculate where the target is, and that will cause him to miss or not hit as powerfully. And be fast. Boxers can move quickly to close the distance. You have to be faster than them.
3) Time your strikes. When he begins to move, that's when you should strike. Don't wait until after he's done before you counter. When he sees you striking, he'll have to change his technique mid-flight. That puts him instantly on the defensive, and it takes time for him to recalculate what to do. Right after he begins to punch is also when he's most vulnerable. His hands and body are not in a defensive position, which means his defense will be weaker, making your damage more significant. And this can really frustrate your opponent, causing him to get sloppy and take more risks which you can take advantage of.
4) Practice take-downs. A boxing posture is more upright and narrow compared with that of MMA or wrestling. It's optimized for a sport where they never have to worry about being taken down. So if you find yourself in a bad position where the boxer has closed the distance with you, that's when you can get in a take-down. The single leg take-down is taught in the first month in most Brazilian Jiujitsu schools. You can find plenty of youtube videos teaching it. Get a partner and train this and other take-downs. They're invaluable against a pure boxer when you find yourself in a bad position (up close). Take-downs are almost never executed "cleanly", so you'll probably end up being pulled to the ground with your opponent. You need to practice with that in mind, getting to your feet as quickly as you can after being pulled down with your opponent. Once on your feet, you've got stomps and football kicks you can do. And you can run away.
In addition to all of the above, I'll just say work on your cardio stamina and general conditioning. Boxers train to conserve their energy. They have excellent cardio stamina. And they're fast. If you want to stay on the outside, keep moving, and move faster than a boxer, then your cardio conditioning must be even better than theirs is.
Finally, I'll forward you to another article I wrote about reaction times which might be useful for you: Defence in martial arts in general
Hope that helps!
Rule 1: No jumping. As soon as your feet leave the ground, you lose control - if he rushes in, you'll go flying.
Rule 2: Kicks tend to be slower and easier to dodge/catch than punches, so unless you have decent training, don't lead with them. A technique that misses is generally worthless, wasted energy. A technique that lets your opponent start grappling or breaking limbs is worse.
Now, a boxer generally only needs to worry about 1 limb on each side of their opponent. If they don't have much experience fighting people who kick, a good way to take advantage of this is... a punch. High jab to the face - making him raise his guard to block - followed by a roundhouse kick or knee strike from the matching leg to the now-exposed lower ribs.
Even then, after the first couple of attempts, they'll get wise to it. Most "street fights" only last 30 seconds or so, but a trained boxer probably has the stamina to go longer than that - if your own stamina isn't up to a drawn-out fight then you need to stay on the offensive and hope to finish fast.
Rule 0: Don't get in a fight. That way you can't lose. The discipline and situational awareness to avoid these situations is a key part of what seperates a "Martial Art" from a "Sport".
This question has already been answered, but I wanted to add some additional basic information.
Try de-escalating the process! You never want to fight, especially not against someone with martial art experience! Chances are high that you will not only lose (this is nearly guaranteed [99%] if you have no experience at all and only luck or a mistake will prevent this), but also take serious damage out of the fight depending on your opponent (some just try to win/end the fight as quickly as possible; some want to make an example).
If you have no other choice, you obviously don't want to fight "their game". Against a boxer, you don't want to try "out-boxing" him.
Be very careful with kicks! If you are not good at kicks and/or kick to high/slow, your opponent will easily counter you. Kicking opens up a big weak point and if your kick doesn't work as planned, their counter-attack almost certainly will! Worst case will be that he catches your leg and kicks away your other leg (which even a normal, non-martial art person can do) and you will be on the ground; if you've ever watched UFC, you should know that being on the ground is a terrible idea.
So, let's say there is no chance of stopping this fight, but you can't simply out-box him since he is the more experienced one. At this point it's worth trying to run away or being very mobile, trying to reach space as soon as possible. The boxer will try to get closer, but as long as you are outside his reach, he will struggle to land critical hits. This still requires you to do some very quick steps and always have your jab hand at head level to turn away punches. It's not important to block them completely, but prevent them from hitting where they should hit. Still be careful; he will soon adapt to your style and also attack your body parts. Even trained boxers are knocked out with a single punch.
Last, but not least, dirty tricks! As far as I know a boxer's stance won't protect his genitals or other critical parts. Boxing has strict rules about attacking the lower areas or human weak points. Attack weak points and use dirty tricks. This will be your best chance against him! A knee-strike to the genitals will stop most men with one hit, no matter their size or strength, and a boxer won't have practised blocking such dirty moves. Spit in his face, since it's disgusting for most people to have such thing in their face and it will bring them out of context. Dirt, sand or even dog mess on the ground? Take it and throw it at him! What's more important? The fact you touched faeces or some serious injuries?