TLDR: The Uchiha Clan were distrusted by the village leadership and were ordered to not engage the Nine-Tails.
As per Itachi Shinden, the Uchiha Clan (which was the Konoha police force during the Nine-Tails' attack) were ordered by the village leadership (Konoha Council) to protect the civilians in the village and not engage the Nine-Tails.
Uchiha Clan members believe that this was because they are distrusted by the village leadership. They also feel that they are being suspected to be what actually caused the Nine-Tails incident.
Indeed, after the Nine-Tails' attack, the Konoha Police headquarters (which sustained heavy damage) and the Uchiha Clan houses were ordered moved to the outskirts of the village, too far from the village center, despite Fugaku Uchiha's protest. (Fugaku is the head of the Uchiha Clan, and Itachi and Sasuke's father.) The location also can be easily spied upon from several vantage points as noticed by Fugaku, adding to feelings of distrust between the Uchiha Clan and the Konoha Council, culminating at the Uchiha Clan massacre.