E.g. サッカーをするのは趣味です playing soccer is my hobby. And サッカーをしているのは趣味です
Because I’ve seen Japanese people use the teiru before a nominalizer such as this sentence , “ あの女性が食べているのは何ですか？” “what is that woman eating” .and it made me wonder what the difference is
by Substantial_Abies841