It is singular to refer to the game. However, a shot may be called a billiard and in that case, billiards can refer to multiple shots and would be plural.
The noun 'billiards' is a mass (uncountable) noun, a type of aggregate noun; a word representing an indefinite number of elements or parts (like news or clothes). The noun 'billiards' is a word for a type of game (singular) takes a verb for singular. The word 'billiard' is an adjective and a noun. The noun 'billiard' is a word for a type of shot in cue sports, not the singular for the type of game.
The word billiards, though plural in form, is singular in meaning. There is no such thing as a billiard. You can refer to a billiard ball or a billiard table, but in those constructions the word billiard is an adjective, not a noun.
practitioner is singular (plural practitioners)sofa is singular (plural sofas)satellite is singular (plural satellites)clips is plural (singular clip)dentist is singular (plural dentists)dollars is plural (singular dollar)article is singular (plural articles)magazines is plural (singular magazine)laminator is singular (laminators is plural)radios is plural (singular radio)
singular and plural
Singular: book / Plural: books Singular: cat / Plural: cats Singular: child / Plural: children Singular: foot / Plural: feet
Are is plural. "Is" is singular. For example, "There is a glove on the chair". That is singular. "There are gloves on the chair". That is plural.
"Has" is singular, e.g. He has, she has. "Have" is plural, e.g. They have, we have. The exception is "I" - e.g. I have.
Here are some examples of nouns that are plural in form but singular in meaning: gallows glasses headquarters news pajamas pants scissors series species billiards athletics physics Philippines measles tweezers dominoes economics civics politics
The word team is singular; the plural form is teams.
Who may be singular or plural.
This is singular. These is the plural form.
These is plural, this is singular