One of the [tag]youth baseball drills[/tag] that I use with my 12 person 9 & 10 year old [tag]baseball[/tag] team is to conduct a scrimmage using the format of 4 vs 4 vs 4.   This works well because I can field an entire infield and a couple of outfielders.

Each team of 4 is competing against each other.
We have each hitting team clear the bases after 3 outs.
Each hitting team is done after 6 outs or after scoring 5 runs, whichever comes first.
The winning hitting team is rewarded with a single dip ice cream cone @ our local ice cream shop.

This [tag]baseball drill[/tag] gets the competitive juices flowing, especially on defense when the fielding teams have to work together to get the hitting team out.   This also is helpful because there is less standing around as compared to a more traditional 2 team scrimmage format.