Both Schwesser and Curriculum say…a short index (meaning iTraxx) position can be used to hedge a portfolio of credits or expoloit an expected increase in market-wide credit risk
But it does not make sence at all, becaus iTraxx increases when credit risk (CDS) increases…so if I am short on index (loosing) and long on credit portfolio (loosing), where is the hedge or gain on credit risk increase?
In CDS terminology, going long means to sell protection. ie you benefit if credit spreads narrow and the iTraxx drops.
being short an index (or a single CDS) means you have bought protection ie will benefit if the index rises.
It is a little bit different because the index moves in opposite directions but the logic is the same as a stock index. Ie if you’re long, you win if things get better, and if you’re short you win if things get worse.