As fields of study, physics and math/maths have no plural forms. Of course, math is short for mathematics. There is another, little used meaning of physic (meaning medicine or to cure) that has a plural form or third-person singular form. I believe the word "sport" is straightforward in usage. "Football is a sport, but there are two major sports called football".

Maybe I am confusing Brits with upper-class white Americans. I remember many people made fun of Mitt Romney when he was running for president, and he commented, "I like sport." He meant sports like polo and yachting. To most Americans, it sounded very snobbish.

Actually, Brits also say 'sports'. I believe Australians sometimes use 'sport' as a familiar form of address, a bit like 'dude'.