Hello Wendy
The word ''sport'' is a noun. It can be used in both singular and plural.
e.g. Volleyball is my favourite sport.
Volleyball and handball are my favourite sports.
There is also the word ''sports'', which is an adjective.
e.g. He is a sports columnist / presenter.
Do you belong to a sports club?
It's the school sports day next Tuesday.
To sum up, ''sport'' is a noun (it can also be a verb) and ''sports'' is both a noun (plural) and an adjective.
Hope this helps :)