Over or Under is a game that is quick and easy to organise
Equipment : Long piece of rope
Time : 10 - 20 Min's
Get 2 leaders to hold the rope at opposite ends of the hall with the rope at a suitable height. Then get all the Explorers to stand one one side of the rope. Explain to the Explorers that they need to run towards the rope and either go over or under the rope without touching it depending on what the leader shouts. If the touch the rope they are out and the winner is the Explorer who manages not to touch the rope.
You can add things to this like reversing the calls so under means over, lower and raise the rope, and maybe move the rope like a skipping rope and get the Explorers to pass through.