implementation
...
type
TDummyDBGrid=class(TDBGrid);
...
procedure TForm1.DBGrid1MouseUp(Sender: TObject; Button: TMouseButton;
Shift: TShiftState; X, Y: Integer);
var
aCol, aRow, xRow : integer;
begin
xRow := TDummyDBGrid(TDBGrid(Sender)).Row; { xrow from DBGrid }
TDBGrid(Sender).MouseToCell(X,Y,aCol,aRow); { arow from mouse }
if (Button = mbRight)
AND (aCol=2)
AND (aRow=xRow)
then
TDBGrid(Sender).PopupMenu.Popup; {popup ONLY over the celected cell}
end;