Get people moving around/energised
Large open space, with set boundaries
One person is designated as "it" and begins a game of tag. One someone is tagged they become "it" as well and must become part of the blob by linking arms with the other people that are it. The blog continues to grow until it has swallowed all the participants.
If not careful the blob can become an unintentioned game of "crack the whip" with people at the end of the blob being flung off. Encourage the blob to move at a speed safe for all participants. This can be fun to watch, a well thought out blob can slowly separate other players and surround them.