What is what kind of dog is in the sandlot?

In the movie "The Sandlot," the dog is a large English Mastiff known by the name of "The Beast." The character of the dog is built up throughout the film as a fierce and intimidating creature that scares the neighborhood children. However, it is later revealed that "The Beast" is actually friendly and playful once the kids have the chance to get to know him. The dog in the film is portrayed as a loyal and protective companion to his owner, Mr. Mertle.