Blue leg crab attacking

[Hanneman24]

I have three crabs that have lived together just fine. Walked downstairs to add two more and all of a sudden two crabs are attacking one crab and one of the new ones started in along with them and the eventually walked away. Is this normal for two crabs against one and for someone new to come in and add to the attack?

 

[areohen]

The crab may be trying to steal the other crabs shell. I've had my crabs fight over shells before. Make sure you have extra empty shells in the tank to help with that