Is it permissible to wear loose trousers with a long shirt for sports, with the desire to adhere to the legal hijab?

The hijab is an obligation upon the Muslim woman by consensus of the scholars. Scholars have not stipulated a specific form for the hijab, but rather have set conditions that must be met therein.

It is not permissible to wear trousers as a hijab unless they are wide and loose, not defining the body's contours, and are worn with a wide, loose top that covers the body down to the knees and below, or if they are covered by something else like an abaya.

Sportswear is permissible for a woman to wear in front of other women, provided it is not tight or transparent.

It is not permissible for a woman to practice sports in the presence of non-mahram men, even if the attire is modest, because athletic movements can be a cause of temptation. If a school obliges practicing sports in the presence of non-mahram men, it is not permissible to continue there, and one must seek a way to be exempted or find another school that does not impose such a requirement.