tldr;
Played pickup sports: baseball, football, street hockey, ice hockey, etc. almost daily after school and all day weekends and Summers from second grade through high school. Often biked or walked for miles to do it. Never any adult supervision.
There's a public park near me now with tennis courts, racquetball courts, a full basketball court, three baseball fields (one large enough for 90 foot bases) and a large open area used primarily for soccer and lacrosse. It's very well kept and in a very safe area. The pickup game I see there most often, almost every day, is basketball. Mostly teen aged kids and often a lot of them. I've seen full court games being played there where kids were on the bench and rotating in and out there were so many. Sometimes you'll see pickup soccer. More often it's kids practicing soccer without supervision. Once in a great while you see a baseball pickup game there but it's usually kids practicing with each other.
I think the reason kids have moved away from pickup sports is mostly (80%) due to parent fear (often unwarranted IMO) for kids safety. Kids just aren't allowed to go off on their own unsupervised and be gone all day. To a far lesser degree IMO it's due to sports specialization, poor and biased coaching in the recreational youth leagues and things like video games and social media. It's the modern parent's prerogative of course but I think kids do miss something from the lack of freedom and in person socializing.
/tldr;
I started playing pickup baseball almost daily during the Impossible Dream run. I lived in neighborhoods in Lowell, Chelmsford and Falmouth where there were a lot of kids around the same age. It seems like families had a lot more kids close together in age then. We played baseball with as few as three players or with three we'd just play pickle. There was never a 1B unless we had six or more on each team. Pitcher was almost always first base. Hit it to right field you were out (LF for an LHH). Normally no catcher either. The hitter just retrieved the ball from the backstop which was quite close to the plate. No walks. Ghost runners advanced the same number of bases as the hitter. They could be forced out if the fielder could get to the bag before the batter reached first. Double plays could happen with ghost runners.
For disputed calls, we worked it pretty much like a possession arrow in basketball. We named it the 'Call.' At the beginning of the game you flipped a coin for who would have the Call first and then go back and forth whenever it was used. When there was a disputed play the team with the Call could opt to have the final outcome in their favor. Once used then it was the other team's Call to use. Led to some interesting strategy to use or not use the Call when you had it. You could always yield the play to the other team and keep it for later in the game.
Once Roberts Field on Old Westford Rd. in Chelmsford was built, we played there almost everyday it wasn't raining from March to September. We played pickup tackle football there in the fall but usually played football in one of the yards. Played a lot of street hockey in the Fall and Winter too when it was possible. I can remember one summer we organized a pickup baseball league where 4-6 kids from one neighborhood would bike miles over to another neighborhood who also had a team and play a game. I played pickup baseball at one frequency or another all the way through high school.
In Chelmsford, I lived in a house with over an acre sized lot. When the house was built (on a corner lot) my father decided to purchase the lot next door as well. The house was set well back from the street and the driveway was flat, straight and quite long. It was two car width so it was a near perfect street hockey 'rink.' We built a couple of nets with 2x4s and fence wire and it was game on, Garth. Played street hockey through high school as well though it was far more intense as players got older. We'd play on this single tennis court and there was a lot of hard and often dirty hitting and hacking. High school street hockey was a bully's dream come true.
In the Chelmsford backyard behind the second lot was an area of near level grass maybe 125-150 feet square. We built a little league size baseball field there starting from the back left corner outward. It had woods behind the 2x4 and wire backstop, woods from the left field line to left center field and woods in roughly the same position in right field. Anything hit fair into the woods was a double. Left center to right center was wide open and led to the neighbor's backyard. This was the everyday field for pickup baseball until Roberts Field came along. We lost a ton of baseballs in the woods.
In the winter there were a lot of backyard rinks. The tough thing if they weren't nearby was getting to them with any amount of gear. Played a lot of pond hockey too, usually without any gear except a stick and a puck. The pond used to be crowded with kids everyday after school and on weekends. Played a lot of what Orr described in his biography as 'shinny.' Basically a huge area of ice set aside and you did a lot of skating and puck carrying playing keep away.
Had a friend who had a built-in pool in the backyard. It really wasn't used all that often in the Summer. It was fairly large, 20x40 as I recall and was all fenced in. In the Fall the pool was partially drained, maybe 12 inches or so and covered with a large black plastic tarp, maybe six mil thick, which covered the entire pool and extended probably six feet beyond the edges. Originally, small sandbags held the edges down. Most of the cover sat flat on the water surface. It would rain or snow and before long the top of the cover was flooded with water. One year we discovered it made a great little rink once the flooded cover froze. The pool area was lighted with floodlights so you could play well into the evening. The first year we played on it with just the sides of the cover protecting the edge of the pool. This did not go well. Pucks would just rip through the plastic and often could not be found until fished out of the bottom of the pool in late Spring.
So the Dad, a talented carpenter although it wasn't his trade, came up with an idea to build boards for the edges of the pool. He screwed together two 2x12 planks perpendicular to each other and then the resulting 'T' shaped piece of wood turned on its side became the edge boards and was also effective as protection for both the edges of the pool and the plastic cover. The T-boards were all connected at the breaks, every 8-12 feet I think, so it was a pretty solid structure all the way around the perimeter. The sand bags were no longer needed either. We'd the flood the top of the cover up to the bottom of the vertical part of the sideboard and wait for cold days. The interesting thing about this pool-rink was it froze to a usable thickness faster than any pond or regular backyard rink and it stayed frozen thick enough to use well into the Spring. In the Spring when the snow would melt we'd find 50 pucks lying all over the pool deck or in the yard over the fence having been previously lost for the Winter when they were shot into the snow banks shoveled off the ice surface.
That pool was used 20 times more in the Winter than in the Summer.
Good times.