Interacting with the map allows you to see which team plays baseball at which park in the United States.
stad_df <- jsonlite::fromJSON("https://gist.githubusercontent.com/the55/2155142/raw/30a251395cd3c04771f29f2a6295fc8849b73d11/mlb_stadium.json")
stad_df[,c(3,4)] %>%
leaflet() %>%
addTiles() %>%
addMarkers(popup = stad_df$team)