republiccitysanctuary:

While Lin’s personality and beliefs are puzzling, let’s not forget that Toph is the one who started the metalbending police force. The real question is how the hell did Toph go from rebel to cop? I have yet to come up with a plausible theory for this one.

I don’t think she was necessarily a cop. I think she trained all the cops and made them awesome. Plus, as she says in The Promise Part 2, she loves yelling at people.