Divide your group into two teams and let each select its own name, such as "Bookworms" or "Word Wizards."
Name a scorekeeper and choose a skilled reader to serve as the umpire to show word flashcards and judge the accuracy of the players' responses. 

Designate specific spots as home plate and three bases.

When players are "at bat," they must state in advance the number of bases they're aiming for.
For a single, they must read a word on a flashcard quickly displayed by the umpire.
For a double, they read the word and define it.
A triple requires reading, defining and spelling.
To score a home run, a player must achieve all three and use the word in a sentence.

The umpire sets a time limit on responses to keep the game moving.
There are no strikes or balls-a single miss constitutes an out, with three outs allowed per inning.
The number of innings is optional.
Post a scoreboard prominently in the classroom and keep a record of each team's "runs" as the games are played.

At the end of the year, hang gold paper medals around the necks of the champs in a festive Olympic-type ceremony.