Yesterday I said something like 'it must be raining, the boys are stopping playing basketball', and I wondered what tense that was. Double present continuous? No such thing....and I couldn't find it online.
I am stopping (the car)(my diet)(John)(playing basketball). In this 'sentence', all the underlined words are nouns.
Nouns can be subjects or objects. 'Playing (basketball) is fun.'
An -ing verb that functions as a noun is a gerund. "playing" in your sentence is a gerund.