This खेल form of the verb is the one that comes before रहा in the progressive, right?
The verm bis खेलना, and yes, if you wanted to make it continuous (He plays) it would be वह खेल रहा है
This ना form of the verb is the citation form, then. It does function much like the infinitive in other Indoeuropean languages.
What kind of verb form is this khel? Can you use the form khelna in this context?