Mantis Shrimp Question

hello! I'm a college student in a marine biology class and I asked my teacher how big a mantis shrimp would have to be to kill a guy. He said it was a physics question so here I am!

So. Assuming the Mantis Shrimp would be striking in the center of the chest of the average American man [175cm tall, 90.26kg, converted to metric system from the CDC website. not sure if it's relevant to know, figured it might help??], how big would the shrimp have to be?