Playing is not an investment because you are not putting your money in the hands of other person/company in able to get profit which is the main definition of investment. By the word itself Gambling, It is just a game that involves many and there is a presence of risk with it. Gambling can be considered as investment if you literally invest on gambling site and get some share with them.
We could call gambling as a investment, in a way. Because in order for us to gamble, of course we are going to invest our money to use it on betting, and that is the risk that we are talking about, it is just either we are going to win or lose, still, it is an investment, but not the investment where we are waiting for something in return surely because it is what it is, I mean, for example is if you are going to invest in the bank, of course you must know first the rules of how the Investment works, if they are really going to make your money double.