Can you give us the actual sentence that you read? I think the context will be important in answering this. Anyhow, the phrase "in the street" refers to only one street. For instance, 1. There are a lot of people standing in the street. 2. A red car is parked in the street. 3. A naked guy is dancing around in the street. The phrases "in the streets" and "on the streets" refer to more than one street. Examples Using In: 1. There were riots taking place in the streets of Boston. 2. Gang members were firing at each other in the streets of Boston. 3. All over Boston, children were playing in the streets. Examples Using On: 1. First responders arrived to help those injured on the streets of Boston. 2. News reporters interviewed a man who lives on the streets of Boston. 3. He tried to help as many homeless people who live on the streets of Boston as he could. 4. Crime is rampant on the streets of Boston. I think "in the streets" is used for things that are temporary / happening in the moment, while "on the streets" has a more permanent sense. For instance, in "Crime is rampant on the streets of Boston.", the crime has been happening for years. but in "All over Boston, children were playing in the streets." the children were playing in the streets on a particular day. Also, the word "on the streets" is more general than "in the streets". That is, "in the streets" sounds like you are talking about a number of specific streets which are in view in some cases. Perhaps another native English speaker could comment on this because I know how to use them but I can't really seem to dig into my brain and give a definite answer as to when either should be used. This is such a hard question to answer. Plus apparently there are differences with their usage in UK and American English. Hehehehe

"in the street" means "in the middle of the street," and "on the street," means "located on the street". For example: I live on 10th Street. The shop is on the next street. and Watch out! There is a tire in the street. I saw a lovely cat in the street this morning.