diff --git a/app/services/statistics_service.rb b/app/services/statistics_service.rb
new file mode 100644
index 0000000..72c2b09
--- /dev/null
+++ b/app/services/statistics_service.rb
@@ -0,0 +1,25 @@
+# frozen_string_literal: true
+
+class StatisticsService
+  def initialize(stage)
+    raise 'Unsupported stage type' if stage.nil? || stage.groups.empty?
+
+    @stage = stage
+    @group_scores = sort_group_scores(@stage.groups, :group_points)
+
+    @most_dominant_score = sort_group_scores(@stage.groups, :scored_points).first
+    @least_dominant_score = sort_group_scores(@stage.groups, :received_points).first
+  end
+
+  attr_reader :group_scores
+  attr_reader :most_dominant_score
+  attr_reader :least_dominant_score
+
+  private
+
+  def sort_group_scores(groups, by)
+    groups
+      .map(&:group_scores).flatten # collect all group scores
+      .sort_by(&by).reverse
+  end
+end
diff --git a/spec/services/statistics_service_spec.rb b/spec/services/statistics_service_spec.rb
new file mode 100644
index 0000000..6e53708
--- /dev/null
+++ b/spec/services/statistics_service_spec.rb
@@ -0,0 +1,54 @@
+# frozen_string_literal: true
+
+RSpec.describe StatisticsService do
+  before do
+    # build tournament with predictable test data
+    tournament = create(:tournament)
+    group_stage = create(:group_stage)
+    group = group_stage.groups.first
+    @most_dominant_score = GroupScore.new team: create(:team),
+                                          group_points: 100,
+                                          scored_points: 100, received_points: 0
+    @least_dominant_score = GroupScore.new team: create(:team),
+                                           group_points: 0,
+                                           scored_points: 0, received_points: 100
+    group.group_scores << @most_dominant_score
+    group.group_scores << @least_dominant_score
+    tournament.stages << group_stage
+    @service = StatisticsService.new group_stage
+  end
+
+  describe '#new' do
+    context 'with a playoff stage' do
+      it 'throws an exception' do
+        expect do
+          StatisticsService.new create(:playoff_stage)
+        end.to raise_error(RuntimeError)
+      end
+    end
+
+    context 'with a group stage' do
+      it 'succeeds' do
+        StatisticsService.new create(:group_stage)
+      end
+    end
+  end
+
+  describe '#most_dominant_score' do
+    it 'returns the most dominant group score' do
+      expect(@service.most_dominant_score.id).to eq(@most_dominant_score.id)
+    end
+  end
+
+  describe '#least_dominant_score' do
+    it 'returns the least dominant group score' do
+      expect(@service.least_dominant_score.id).to eq(@least_dominant_score.id)
+    end
+  end
+
+  describe '#group_scores' do
+    it 'returns an array containing all group scores' do
+      expect(@service.group_scores.length).to eq(GroupScore.count)
+    end
+  end
+end