I like to link my warm ups as far as possible with the rest of my lesson, so here is a very quick warm up ideas when teaching Net and Wall lessons, such as volleyball and basketball.
The following warm up work really well in bad weather and are designed for children to mobilise the various muscle groups, that they will be using in the lesson. I normally do the next few warm ups as a set.
The Over and Under race
Children start lined up in teams like they would for a relay. The first person passes it under their legs to the person behind them, who passes it over the top of their head to the person behind them, who passes it under their legs and so on. When the ball gets to the back, the back person with the ball runs to the front and starts again. This is repeated, until the class has got back to the beginning again.
You can then repeat this race again, but this time the children pass the ball turning their body to the side to pass it to the person behind them. The next person turns the opposite way and repeat till the first person gets to the front.