Thanks Valentina Moseychuk for another warm-up idea which will work best for large groups 6
Players are broken into small even-numbered teams (3-4 players each) at the baseline. Each team has one ball to be used as a baton would be used in a relay race. Teams compete to be the first to have all players race to the net and back.
Here it is in Valentina's video. This activity is at 1:36. BTW the video is worth watching for the crazy fun soundtrack alone!