For participants to practice throwing and catching tennis balls, and use those tennis balls to spell words and add numbers.

Other Skills:
Coordination

Give each participant a tennis ball (that has a letter and number on it).
Divide the group into teams of approximately 6-8 participants.
Set up hula hoops at the corners of the gym for each group.

Warm-Up

Each participant will have a tennis ball (with a number and letter on it).
Divide the group into teams of 6-8 participants.
When the leader gives the signal, participants will pass their ball to members of their group. Remind participants to call the name of the participant they are throwing their ball to before they do, to make sure they are looking.
When the leader says "Stop" or blows a whistle or stops the music, participants will look at the ball they have in their hand and if they have an odd or even number.
Designate an activity for odd numbers and even numbers. If odd number's activity is jumping jacks and even is squats, then all the participants with an odd number tennis ball will do jumping jacks and even will do squats. Do the activities for approximately 30-60 seconds each.
Have participants start throwing their tennis ball to their group members again.
Stop play, and designate new exercises for odd and even numbers. Allow participants to come up with exercises.

Tennis Ball Spelling

Divide the group into 4 equal teams (you can use the groups that were used for the warm-up).
Each group will have a "Spelling Bee Hoop" (hula hoop or pylon) at a corner of the gym, or outside the playing area.
Could also have a piece of chart paper and marker next to each hula hoop.
Give each participant a lettered and numbered tennis ball, and have them start at their "Spelling Bee Hoop"
When the leader gives the signal, participants will scatter around the play area tossing and exchanging their tennis balls with all participants, not just participants in their group.
When the leader gives the signal to stop, each participant will take the tennis ball they have in their hand and bring it to their "Spelling Bee Hoop".
Groups will have around 45-60 seconds to create as many words as they can with the letters on their tennis balls. They can write their words on the chart paper or place the tennis balls to create the word.
After 45-60 seconds are up, the leader can go around and ask each group to say 1 or 2 words they came up with.
Participants now start to toss and exchanging the tennis balls again.
Go for around 4-5 rounds.

Instead of having groups, have participants create words with any participants in group. Have participants try to create long words.
Instead of spelling words, when participants bring their balls back to their area, have them add up all the numbers. Or, depending on the age group, have them put them from highest to lowest, or separate even and odd numbers.