Volleyball has 6 field-players per team.

They don't do that in professional matches, but for fun matches it's perfectly normal to play with less people to even things out.
There's a formation how to play with a team of 6.
There's a formation how to play with a team of 5.
There's a formation how to play with a team of 4.
There's a formation how to play with a team of 3.
There's a formation how to play with a team of 2.

If there's one team of 8 players and one team of 11 players, why can't the bigger team just play with 3 people less?

and they used to play three girls on half of the court with three girls on the other half court. Our team had more members, but they all skipped practice so when it a couple of the girls fouled out of the game the coach decided that he would only have two girls in each half court. Even though we were playing four versus six, our girls still managed to extend their lead on the other team.

Now that it is a given fact that violent sports like football can cause brain damage even if a person doesn't suffer a concussion, more and more boys and their parents are a lot less likely to want to play.

The long term costs and effects are simply too high.

That plus the huge movement into the cities and away from rural areas drain the available pool of boys. While Iowa's total population grows very little, Des Moines and suburbs are exploding, Iowa City and environs are exploding while rural counties continue to decline in population.

I thought it would take longer, but the Friday night football games in rural Iowa may soon go the way of 6-on-6 girls basketball.