Position of first element in list which is repeated

firstDup = Min @* Map[Rest] @* Values @* PositionIndex;;

firstDup @ {{-1, 0}, {-2, 0}, {-3, 0}, {0, 0}, {-2, 0}, {1, 1}}

5

firstDup @ {{-1, 0}, {-2, 0}, {-3, 0}, {0, 0}, {-2, 0}, {1, 1}, {-2, 0}, {-2, 0}}

5

firstDup @ {{-1, 0}, {-2, 0}, {-3, 0}, {-1, 0}, {0, 0}, {-2, 0}, {1, 1}}

4

If you just want the position of the first duplicate element you could use something like this,

firstDuplicatePosition[list_]:=With[{ds = CreateDataStructure @ "HashSet"},
    Catch[
        MapIndexed[If[!ds["Insert",#1],Throw[#2]]&, list];
        {}
    ]
];
firstDuplicatePosition @ {{-1, 0}, {-2, 0}, {-3, 0}, {0, 0}, {-2, 0}, {1, 1}}
(* {5} *)