The Quality Assurance Team (QAT) was responsible for maintaining quality of ranked beatmaps. Because its responsibilities gradually shifted from quality assurance to mapping community maintenance, the group was renamed to the Nomination Assessment Team (NAT).
The QAT was created as part of a manual trial for modding v2 attempting to automate BAT promotion and retirement. The team reviewed Qualified beatmaps and would disqualify those that did not meet the ranking criteria or the team's personal quality standards.
The QAT's reputation among mappers and players was mostly negative in response to frequent disqualification of maps that users believed were going to be ranked. Players were mostly displeased with the loss of performance points and mappers disagreed with the QAT's enforcement of restrictive quality standards.
In 2016, the QAT began reactively disqualifying beatmaps based on user reports rather than proactively reviewing beatmaps for disqualifications. This led to most of the QAT's tasks being management related, such as evaluating Beatmap Nominators (BN) and reforming the ranking criteria.
The first QAT Leaders were established in 2017 to allow communication between the QAT and osu!'s developers after Loctav's leave from the team.
Quality assurance was still part of the team's responsibilities, but it continually became less of a focus point as members of the BN took the primary quality control position.
In 2019, it was deemed that the QAT was no longer capable of fulfilling its initial quality assurance responsibilities, so the group was renamed to the Nomination Assessment Team.