Why do you say do judo not play judo?

Answer 1

You say "do judo" because it isn't usually casual, and doesnt require a team, just two people. Such as you play football, but you do Karate. The term of "i do" is usually refered to any martial art that is practised, rather then "i play". This could be related to the feeling that to do something is to work and improve, while play is more casual.

While this is true, I disagree. Judo is a sport, a most well known sport at that. And much as you would say play football, you are playing judo as well. Yes, playing is casual, BUT it is used to describe a sport or game, such as judo. Using the term play just like you would say that you play Chess, not do it. While you play judo though, it would be like playing in a Baseball game, while you would practice to work and improve your skills. Just like at a tournament you would play judo, at a class or in a Dojo you would practice it.