How to remove all default resolvers from a Play! application?

Turns out the answer is to use the correct sbt syntax.

The code listed in the question is generating configuration for the build, but not assigning it anywhere. I believed the := replaced the global config for the resolvers key, but it does not.

Putting the following in project/Build.scala forced the Play app to resolve dependencies from our internal Nexus:

val nexusResolvers = resolvers := Seq(
  "Maven Central (proxy)" at "http://repo-1/nexus/content/repositories/central/",
  "Typesafe (proxy)" at "http://repo-1/nexus/content/repositories/typesafe-releases/",
  // some more internal Nexus repositories
)

Note assigning the result of resolvers := to a new val, which is then added to the settings of the project in the same file:

val main = PlayProject(...)
  .settings(nexusResolvers: _*)

Also, got rid of the sbtResolver and externalResolvers parts of the config, which had no effect.

Edit or create /home/YOUR_HOME/.sbt/repositories add the following:

[repositories] local my-maven-proxy-releases: http://nexus_domain_or_ip:8081/nexus/content/groups/public/

when running play add this parameter: -Dsbt.override.build.repos=true

e.g: activator run -Dsbt.override.build.repos=true

This prevents play from loading the repositories defined in project configs.

See this for details.