Draw a baseball diamond and a score board on the board. Students, in turn, are at bat and choose how difficult a question to attempt: a single, double, triple, or homerun. If a student answers correctly, s/he moves ahead the appropriate number of bases. The students who are already on base advance the appropriate number of bases. Players who advance to homeplate score a point for their team. If a player answers incorrectly, s/he is out. Once a team makes three outs, the other team is up. This works well with spelling practice because it is fairly easy to compile lists of easy to difficult words.
Note from Steve Mendoza I teach at a Japanese high school, and I have some additional ideas for the game Baseball 2?. It may be a good idea to use playing cards, i.e. ace = single, 2 = double etc. Also the joker card can be an automatic walk, and king can be an automatic strikeout. The cards are put face down and the students pick one randomly. This adds a more random element to the game. In Japan, most students would just pick single each time, if given the choice.