First the brief study of sports part. I did some thinking once, and came to the realization that, George Carlin notwithstanding, all sports boil down into three basic types, plus combinations of those three:
1. Get the ball in the goal
2. Eliminate the opponent
3. Get there first.
As an example, golf is a pretty basic example of getting the ball in the goal. Boxing has as its goal to eliminate the opponent. And racing is an example of getting there first. Some games, as I mentioned, are combinations of these. Baseball is a combination of eliminating the opponent (outs) and getting there first (rounding the bases to home plate) with a ball included to give the other team something to do (this could be considered a manifestation of getting the ball in the goal).
What I did was took the three basic ideas, combined them on something very similar to an American football field, and came up with tagball. Tagball is essentially a version of baseball, played on a football field.
Two teams face each other, lined up similarly to American football. The offensive team starts with a ball, and serves it (a la volleyball) to the defensive team. Once the defensive team has the ball, the action commences. One offensive player, called a runner, has to make it to the goal at the other end of the field. To stop him, a defensive player has to run up and tag him with the ball. The defensive players can toss the ball around all they want, but they aren't allowed to physically touch the runner other than with the ball. Contrariwise, the offensive players aren't allowed to touch the ball. The runner has four chances to make the goal, and if this is not achieved during his team's turn, then the teams switch offensive and defensive status. Upon reaching the goal, the runner's team scores some number of points, and possibly has an opportunity to score extra, before the teams switch.