Knowing how to fight boils down to understanding your technique distances and timings. Next, is selecting the appropriate techniques in the context to defeat your opponent. Creatively linking together techniques to frustrate, counter, and essentially shut down your opponent is the key to victory.
Tae Kwon Do is fought at a longer range distance. Its timing is relatively slow compared to boxing. Boxing is shorter range and is much faster. In terms of safely learning the essentials of stand up striking sports, I think Tae Kwon Do is the most accessible. I define accessible in terms of chance of injury and severity of consequences of mistakes.
I can't think of anything quite as dynamic a sport as combat sports. It is a 1-on-1 sport and it is as much mental as it is physical - if not more. At a certain level, it's not the techniques that differentiate the good and great athlete, it is the mind and the ability to execute.
Take Street Fighter the video game for example. All the techniques on all the characters remain fixed. You cannot change the techniques. It is the selection of techniques: getting the right distance, anticipating, countering, and forcing your opponent to make mistakes as you gain the advantage. Yet, instead of health bars, we use points; and instead of remote controllers, our body is the controller.
Controlling your own body with great speed, precision, and dexterity and tuning your mind and body to act quickly and to seamlessly make decisions in scenarios of pressure and fear.. I cannot think of a more exhilarating and fun sport to play.
I do not believe the benefits of martial arts are boiled down to how useful it is in a fight. I do not anticipate my students or I provoking or engaging in street fights. But when it comes to learning how to fight, and enjoying the sport, with minimal risk, I can think of no more accessible and fun sport to learn than Olympic style Tae Kwon Do sparring.