He is over-stimuated by an attack of a rival on "his" territory. He is both reinforcing the idea that this house is HIS! and alerting the members of his "colony" that there is an attack that needs to be responded to.

When cats reach a certain point of aggitation they seem to have to express it physically. You might try to distract him with a stuffed toy upon which he can demonstrate how he would repell the invader.... He is responding as a protective cat. Unfortunayely this is one of those spots where cats and humans don't quite match responses.