This fun warm-up is from www.tenniscoachblog.com. Better with six or more players. Players stand in a circle facing in. One player is designated as It. Player who is It has a ball, hands it to player next to him/her and leaves his/her spot in the circle to run around the outside of the circle. Goal is for this player to run around outside of circle and return to his/her spot before ball is passed around circle and returned to same spot. Player should use the shuffle step to run around the circle.
TennisCoachBlog has a video of this activity here if my description is unclear.