Yes, it is. This is a form of atonement for the tribes that would become Shi'a letting Husayn ibn Ali go to his death in the "Battle" of Karbala - it was 71 men and boys versus 30,000 trained troops, so the outcome wasn't in doubt unless they got help that they were refused.
The deal is that the house of Ali was the one the Shi'a recognized (and still do) as the only legitimate heir of Mohammet, hence the only legitimate Caliphs. They let their boy down and have been cutting themselves over it ever since.
Yeah, "battle," more like an assassination with collateral damage.