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My theory is: we adults dont play that much due to our abilities of thinking about the purposes or our exercices. — musicpianoaccordion

When you put it that way, I think the reason why Adult don't play that much is because WE DO know our purpose whe we play, which is according to Google "....engage in activity FOR ENJOYMENT"

As an adult, we think of many different think, there are many priorities, many target, and many desire. Most of the time, we, as adult put aside "Enjoyment" for "Productive Works". Example : As adult we choose to go to work at the day, sleep in the night (or morning :D), and play only in between.

You make a point for "Hopscotch", and you said, they play Hopscotch to be good at certain things. If we think children will do something because they want to be good at certain things, then as parent, making them study would be easy. But it's not, he reason children play hopscotch is because at their age, Thats makes them happy. We as adult don't play Hopscotch because, Hopscotch don't make us happy anymore, "Playing with social media / Computer games, Etc" makes us more happy.

So I think the reason of why adult don't play that much because we put aside our priorities to be "Relaxed and happy in enjoyment" most of the time.

I discussed play with a professionals — musicpianoaccordion

A musician, an actor, a philosopher, a grand master, a sportsman, or an engineer?

I like the engineer's answer, that play is freedom of movement. Perhaps freedom from purpose covers a lot of ground; "the play's the thing" refuses the question 'what for?' and insists that there is no purpose outside the play.

Someone said to me 'To you football is a matter of life or death!' and I said 'Listen, it's more important than that.' — Bill Shankly

The adults I bother to spend time with play plenty.

I find that play is very much about being here and now. Adults plan and children play. As adult we do both. I mean, some Children plan as they grow older but not like us adult (I am aware of handicapped adults but kan refering to those of normal IQ)
It seems that we can play with our minds.
Why not even call this discussion some sort of play?

The problem lies in the perception of the individual. This discussion assumes that the definition of 'play' is downplayed by knowing the practical purposes beyond enjoyment or recreation. However, I believe that it boils down to the main or primary purpose for the action.

For example, dancing. If I were to dance around in the hallways of my school for the sole reason that I want to swing my arms around, then that is play. If I were to practice box waltz for my upcoming formal meet, then that would be something other than play.

Put simply, the definition of 'play' is subjective and is purely reliant on the purpose or reasoning for doing the act.

How do the famous philosophers define "play"?

You might look at Wittgenstein.

My theory is: we adults dont play that much due to our abilities of thinking about the purposes or our exercices.
What are your thoughts on this? — musicpianoaccordion

If adults are not playing much, then IMV they are missing out bigtime. I think that many couples engage in verbal play. It's highly complex, so that I can't just lump it into joking around, though laughter is part of it.

And then sometimes, if we are lucky, we can experience our work as play. My career fluctuates. But even the boring parts increase my ability to play when the parts I like return.

Finally, even serious philosophical discussions can feel like a kind of play.

I play tennis when I get a chance. It serves the purpose of exercise and also the development and practice of skill. My favorite opponents are very close in skill to me. We split winning about half and half. Play also makes you forget the more stressful aspects of daily life. Like us, dogs and cats love to play also. So most if not all higher mammals share this in common.

Homo Ludens is a book written in 1938 by Dutch historian and cultural theorist Johan Huizinga. It discusses the importance of the play element of culture and society. Huizinga suggests that play is primary to and a necessary (though not sufficient) condition of the generation of culture. The Latin word Ludens is the present active participle of the verb ludere which itself is cognate with the noun ludus. Ludus has no direct equivalent in English, as it simultaneously refers to sport, play, school, and practice.[2]

Stop talking about playing and just play. Play with a cat. Play with a dog. Play with a child. Play with an adult. Play. Then quit screwing around and get back to work, or you're all FIRED.

Is the book something to read or just crazy intellectual thought of an author?