This article is from the Mastiffs Breed FAQ, by mmcbee@access.mountain.net (Mike McBee) with numerous contributions by others.
Mastiffs, with their gentle natures, do not have the
instincts that dogfighters are looking for. Their protective
instincts make them actually the opposite to the aggressive
fighting personality. However, they will, at times, fight
among themselves, or with other dogs, for the typical canine
reasons such as pack dominance and sexual competition. Two
190 pound adult male Mastiffs in combat for pack leadership
can be next to impossible, as well as exceedingly dangerous,
to separate.
 
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