This is a great little football warmup if the teacher has taught the students how to throw, catch, and carry a football properly.
Person on one end of the relay line throws the ball to the receiver on the other end. Kids in between are in pushup position. When the receiver catches it, the pushup kids drop down to their stomach and ball carrier tucks the ball in and "high knees" over the classmates on their bellies.
Students on their stomach should make sure there is enough space for the ball carrier to step in between them.