For today, or yesterday rather, I will talk about walking. Yes, walking.
You know when you're running and you just want to stop and walk for 5 seconds? You know, when your muscles are aching and your breathing isn't catching up to your pace, and you are just sweating away? Yeah, that moment.
So, I believe that there is nothing wrong with walking. Yes, it slows you down, but it isn't worth anything to injure yourself, as I have said many times before. If you are past your limit, you should definitely give it a rest.
Also, people believe that walking isn't an exercise. But I believe that it is. It is easier on your muscles, but if you walk too much, it is also bad for you. You may not even realize it, the strain and everything, but it is always there.
So, walking is definitely "okay" to do, and it is most definitely a sport.