Brawl is an option for a different style of Commander game. Brawl games use the normal rules for the Commander variant with the following modifications.
February 4, 2011 · Mirrodin Besieged
rule 903.12a not present in this release
October 1, 2010 · Scars of Mirrodin
A player that’s been dealt 21 or more combat damage by the same general over the course
February 1, 2010 · Worldwake
A player that's been dealt 21 or more combat damage by the same general over the course of the game loses the game. (This is a state-based action. See rule 704.)