It called a Robin because its breast is red, even though it is not related to the European Robin. It is called American because it is found in America. (Similarly birds like Magpie Larks and Magpie...
It was probably a territorial or food dispute between two males.
The american robin is actually a type of thrush, wheras the european robin is a true robin.
Cats -- domestic, feral, lynxes and bobcats -- predatory birds such as hawks and occasionally owls, perhaps the occasional lucky snake.
The American robin is Turdus migratorius. The European Robin is Erithacus rubecula