A sports hall is a sufficiently large single room, typically enclosed with walls and ceiling, that is suitable to exercise one or more sports indoor. It might contain subordinated locker/changing rooms, showers, and a depot room for devices. It can be a standalone building, or part of a larger building.
A sports hall can often be found on a campus of a school, as part of a school building, or in a sports centre.
In some parts of the world, such sports facilities are called gym or gymnasium, however these values are discouraged in OSM since they have a multitude of different meanings.
A facility that is used as a sports hall is tagged with leisure=sports_hall. It can be purpose-build, or converted from another usage.
The building type is described with the building=* tag, thus a purpose-built hall would be tagged building=sports_hall, while e.g. a converted industrial building remains building=industrial.
Use the sport=* tag to describe the kind(s) of sport(s) the sports hall is equipped for.