“Heel” is a pro wrestling term to describe “evil” or “dirty” fighting wrestlers. The opposite is called a “face” and are the good and fair ones. Many wrestlers have had both personas if there career is long enough.
Having not read the rest of this series yet, I'm gonna be honest-
This is nervewracking. It's nothing short of tragic that the two biggest badasses in the entire tournament have to eliminate each other at the top of round 2.