Hey Yuji, how are you? Firstly, you should know this: 1) If you wish to state that ''playing sports'' (your hobby) was an action that happened regularly in the past (but does not happen at the present time), so you should use ''used to''. 2) If you simply want to say that ''playing sports'' was an action that happened at a moment in the past (for example, ''yesterday'', ''a week ago'', ''the other day'', etc...), so you should use the verb ''play'' in its past form. However, as regards the meaning you are intending to convey here, I would say that it is much more preferable to use the idiom ''used to'' rather than simply use a verb in its past form. Please, have a look at the explanation provided below: >> Main meaning: If something ''used to'' happen, it happened regularly in the past but does not happen now. Similarly, if something ''used to be'' true, it was true in the past but is not true now. E.g.: ''She used to go swimming every day.'' E.g.: ''I used to be afraid of you.'' >> ''Used to'' in negative structures: In conversation, you can say that something ''didn't use to'' happen or didn't use to be'' true. E.g.: ''The house didn't use to be so clean.'' E.g.: ''I didn't use to be that smart.'' >> You can also say that something ''never used to'' happen or be true. E.g.: ''Where I lived before, we never used to have posters on the walls.'' E.g.: ''When younger, he never used to have his own privacy.'' >> You can also say that something ''used not to'' happen or be true. This is a fairly formal use. E.g.: ''It used not to be taxable, but now it will be subject to tax.'' E.g.: ''This watch used not to be so expensive as it is now.'' Hope that helps! Should you have any further questions, do not hesitate to contact me. I should be delighted to help.

Nice explanation

Luiz gave an excellent answer. Here are variations of your phrase: - [When I was in school,] I would play sports as a hobby. (maybe I still do, maybe I don't any more) - [When I was in school, ] I used to play sports as a hobby. (but not any more) - [When I was in school, ] I played sports as a hobby. (habitual action - known from the context) - [Yesterday,] I played sports. (non-habitual action - known from the context) For more information, consult English Grammar in Use 4th ed. by Murphy (Cambridge). I believe a PDF can be found on the internet. Lesson 18 (p. 36) - used to (do) - a state or habitual action in the past that is no longer true Lesson 36C (p. 72) - would (do) - a habitual action in the past

Both are correct. The second would be more common though, especially in conversation.

Both are correct. The second would be more common though, especially in conversation.