draw a line in the sand vs take up the gauntlet

To lay down a challenge; to provide a test of commitment (often one which carries a high risk) to a cause. 

To create a real or artificial boundary or distinction between (two places, people or things). 

To indicate the threshold or level above which something will become unacceptable or will provoke a response; to create a boundary and imply or declare that its crossing will provoke a (negative) response. 

To accept a challenge.