.htaccess rewrit rule remove trailing slash if not directory

Question

I know there are many similar questions like this,but I don't understand rewriterule.

I have a php file ,like the following

switch($_GET['p']){
    case"home":
        echo"<a href='sport'>sport</a>";

        switch($_GET['a']){
            case"sport":
                echo"This is sport";
            break;
            }
        break;
    }

I want if access sport case, like

tes/category/sport

NB: tes, is directory of my php file