(Giya!)
A group of pitiful goblins was seen running from a larger group of goblins. A situation like this rarely happens, but once it does, it is always related to two evolves with similar strengths within the tribe.
Whenever it happens, the two would likely battle to their death for the ruling rights over all goblins in the zone, whether they're part of the tribe or vagrant goblins. There are no rules on how the battle would ensue, but it is always done through a brief one-on-one battle or trickery.
Even if the fight was conducted unfairly, it was not the goblin's main concern. To these monsters, only the victor has the right to rule over them.
While killing the loser wasn't compulsory, most winners would choose to do so to ensure the longevity of their reign.