Hold your horses

This is a tag-team wrestling match between a pair of elephants and a pair of horses. 

The elephants have the obvious advantage in size and strength, but the horses are too excited to realize this and they want to get in there and fight. Their manager sees the danger and wants to change his mind, so he’s holding his horses back from fighting the elephants. 

You usually say 'hold your horses' to tell someone to stop doing something because they are going too fast and could face a problem. Here's an example: 

I'm so excited about this concert!
Me too. I'm really looking forward to it. 
I hope it isn't sold out.
Two tickets for the front section, please.
Hold your horses, Mike. Have you seen the prices?
Oh, they're pretty expensive. 
Right. We won't have enough left for a taxi home.
Okay. Let's get cheaper seats.