When the gates open, both creatures are allowed to size up each other without attacking. That's why we have to chain up Pipsqueak. If it strikes during the size up the fight is off, and you lose. If you think the other creature is just going to maul yours, you can ask for the fight to end there. Likewise, if your animal runs back to its pen, that is counted as a forfeit. Some people just use intimidating creatures to force creatures to choose to forfeit during the size up.