I have a deep disdain for large crowds. That’s why I hesitate recommending free concerts and free movie screenings at parks and large public spaces. The crowds are just way too large and the bathroom situation is painful.
Here are some alternatives:
A “local” place that has a large backyard/patio setup. These are usually neighborhood beer gardens found in Brooklyn and Queens. The key is finding a highly localized venue so it won't be tourist infested. Queens and Brooklyn will always be less crowded than Manhattan.
My favorite is ICONYC (pronounced “iconic”). They have a large patio area with lots of picnic benches. ICONYC is a brewery and surrounding the patio area are other food establishments.
If you want live performances, in the same area is Fifth Hammer and Culture Lab. Fifth Hammer is basically a brewery that looks like a giant open garage and has live jazz performing from the street a couple nights a week. Culture Lab has free summer concerts on the weekends. Again since it’s so localized, not a lot of people attend compared to a Manhattan venue (photo above).
The Bohemian Beer Garden is another fun place to hang out at and sometimes they have performances. This is in Astoria and is the oldest beer garden in the city.
If a music concert is in an enclosed area in a park (like Prospect Park), you can picnic close enough to hear the music. 😊 It’s such a broke-New-Yorker hack, but not a bad way in avoiding the crowd.
In the photo: A neighborhood concert at the Culture Lab.